last updated - Apr. 19, 2012
As a materials scientist with an interest in applied mathematics, semiconductor physics, biomaterials, and nanotechnology, my research is very interdisciplinary. My research has its theoretical basis in materials science and applied physics, looking into both fundamental questions such as the growth and formation of nanostructures and also applied questions such as the characterization and use of nanowires and new microscopy techniques.
My research focuses on the creation, characterization, and uses of nanomaterials. The most significant of my contributions to scholarship have been:
1. Creating novel ZnS one-dimensional nanostructures and characterizing them and their growth mechanisms. This included a review article on the topic and 6 journal articles.
2. Developing whisker growth theory as it applies to one-dimensional nanostructures being grown by vapor deposition techniques, allowing also for the explanation of secondary growth on the nanostructures (such as nanosaws, nanocombs, etc.).
3. Developing novel metrology techniques for semiconductor and nanoscale characterizations including method for using hybrid metrology, reference measurement calibration, and using fractal dimension for characterizing roughness.
4. Developing awareness of and framework for thinking about nanotechnology and military applications, including several talks and papers outlining how nanotechnology represents a different approach to thinking about the role of technology in society.
5. Publication of “What is Nanotechnology and Why does it matter”, in collaboration with philosophers Patrick Lin and Fritz Allhoff, a tome which explains nanotechnology as it is practiced today, with a focus on the materials challenges, and then explain the role that nanotechnology will play in shaping many different areas of society.
My primary work has been in developing techniques for creating and using nanomaterials and nanoscale structures in devices. As a graduate student, I worked in Dr. Zhong Lin Wang’s group at Georgia Tech, developing processes and scholarship leading to the inclusion of piezoelectric nanowires in nanogenerators.
Current and Future Research
My research for the last few years has been in industry (for Cree and IBM) and has focused on developing the growth, characterization, and implementation of nanomaterials into LEDs and semiconductor devices. This has involved developing new techniques for creating nanoscale materials, such as InGaN quantum dots and quantum wells, and also new techniques for characterizing materials and surfaces using new microscopy and data analysis methods. The main techniques that I have used for creating nanoscale materials are vapor deposition techniques such as MOCVD, PVD, and ALD. I have developed new microscopy techniques with electron microscopy, scanning probe microscopy, and optical microscopy techniques, particularly as they relate to semiconductor devices. As a researcher for IBM, I have also regularly been involved in discussions involving developments in nanotechnology. These include developments with DNA origami, atomic scale magnetic memory, and silicon photonics.
This work is important because of the growing role of nanotechnology and nanoscale engineered materials in devices ranging from semiconductors to microelectromechanical systems (MEMS). For example, DNA origami, in which controlled folding of single stranded DNA is used to scaffold nanomaterials such as Si nanowires, offers a promising post-lithography route for smaller semiconductor devices. Recent reports have pressed the importance of new materials in fields ranging from energy to drug delivery. For example, the use of one-dimensional ZnO nanowires, aligned along the <01-10> axis so that their piezoelectronic properties are accentuated, are being developed as “nanogenerators” able to transform the energy ambient motion into electrical energy. Controlling the synthesis of the one-dimensional nanostructures is important to their further use of wurtzite nanostructures and applying them. It is also important to their use in multi-component systems (i.e. systems of structures containing more than one type of material – CdSe/ZnS or ZnS/SiO2 nanowires) and in hierarchical structures (i.e. structures with more than one growth type and phase connected in one larger structure). The research that I will pursue would continue and expand on the body of work that has been researched on wurtzite nanostructure. It would expand to include other wurtzite structures such as GaN and work to control the synthesis of nanowires with respect to their length, synthesis site, and other dimensional factors. Not only will this help with understanding the mechanisms behind the synthesis of these materials, but it will contribute to the easy use of wurtzite nanostructures in electronic applications and systems. Using wurtzite nanostructures allows for a leap forward in nanoscale devices and functionality, because of the unique properties of the structure.
Another important aspect of work with wurtzite nanostructures is functionalizing the surface of the individual nanowires. Complex architectures, sensing applications, and other uses of ZnS and GaN nanowires all rely on the successful functionalization of the surface. Sensing applications, both chemical and biological, will benefit from the functionalization of the surfaces. Though some sensing of chemical species can occur without the benefit of functionalization, chemical species adsorbed onto the surface of the nanostructure will enhance the sensitivity and the specificity of the sensor.
Surface functionalization will also be useful in developing complex architectures of nanostructures. For example, well-placed single strands of DNA on the surface of nanostructures could allow for the self-assembly of multiple nanowires into very complex architectures. Developing selective functionalization, with respect to both the species functionalizing and the material/crystallographic face being functionalized, will be a boon to the use of nanostructures in devices.
The difficulty with functionalization is two-fold. First, an appropriate species must be found to adhere to the surface of the nanostructure through a method that does not degrade the properties of the material. It is preferable that the species can adhere to specific surfaces. Second, an appropriate functionalizing species for each material must be found that has specificity for other species and successfully adsorbs to the nanomaterial.
Most wurtzite materials are also very useful in luminescent applications. GaN has been used extensively in LED applications and ZnS is the top material for electroluminescent display applications. The development of the luminescent applications of these materials in nanoscale structures will be an important development and provide many unique applications. For example, a nanoscale UV source could be used in biomedical applications, targeted in vivo.
In order to utilize the luminescent and phosphorous properties of these materials, it is important to develop doping of the materials. One method for doing this is ion implantation. Another method is introducing doping species during the synthesis of the nanostructures, as is done in the current growth of Nitride LEDs. Further, luminescent structures require somewhat complex layered structures. For example, a ZnS-based ELD uses the phosphorous ZnS surrounded by an insulator on either side. Recently, ultra-long ZnS nanowires have been synthesized. With the use of gold and ITO electrodes and proper doping, these could be used in electroluminescent displays.
For the next step in my research, I am planning on integrating my nanomaterials synthesis and characterization research and knowledge with device development, in particular MEMS/NEMS and sensors, with an eye towards energy optimization and creation. With nanomaterials, I am particularly interested in the synthesis of semiconductor one-dimensional nanostructures, such as Si nanowires or II-VI semiconductors, due to their wide range of potential uses. I am also interested in integrating these synthesized nanomaterials with macromolecules, such as DNA, and using techniques for organizing the nanomaterials in device orientations, such as DNA origami. This will involve integrating II-VI nanowires and nanoribbons into MEMS devices. I am particularly interested in pursuing the integration of piezoelectronic nanowires (such as ZnO nanogenerators) into MEMS devices that utilize moving liquids to transfer power – in particular, MEMS devices using photoelectrowetting on semiconductors.Back to home page