PIRE I: 2006-2010, OISE-0530220
U.S.-JAPAN Cooperative Research and Education: Semiconductor Nanostructures and Carbon Nanotubes for Nanophotonics
As science and engineering become increasingly international there is a pressing need for US universities to develop research and education programs to produce globally aware scientists and engineers. This PIRE program was organized around a research topic that the PI and Japanese collaborators had successfully pursued prior to the PIRE collaboration. In addition to training students in research, we provided an array of educational opportunities for students at all levels. One of the objectives is to attract young undergraduates to the emerging areas of electrical engineering and the physical sciences, especially nanotechnology. In the long term, we aimed to increase the number of US students who choose to go to graduate school to study science and engineering.
Our research program investigated the ultrafast and nonlinear optical properties of quantum structures based on the 6.1-angstrom III-V semiconductors (InAs, GaSb, AlSb). These semiconductors are nearly lattice-matched (with lattice constant ~ 6.1 angstrom) and can be epitaxially grown to form heterostructures. Though they possess promising properties for application in next-generation devices, there had been little exploration of their optical properties, especially in the time domain and at high laser intensities. Various optical spectroscopic methods were used to study charge and spin dynamics. These studies not only increased our understanding of the states and dynamics of interacting electrons but also provided new insight into which structures are optimum for specific applications.
The objectives of our tiered and targeted educational activities were to:
- Foster interest in nanotechnology as field of study among freshmen and sophomores
- Prepare junior and senior students to become the next generation of graduate students in nanotechnology and engineering
- Add to the skill set of active graduate student nanoscience researchers
- Create students who are internationally savvy and have a specific interest in Japan
- Educate students in culture, language and technology
We collaborated with other Rice colleagues and leveraged existing Rice programs funded by the NSF. We also used the Rice-developed Connexions framework to increase the educational impact of this project by openly distributing content to a global audience.
We formed a unique, interdisciplinary team, consisting of co-PIs with an extremely wide range of backgrounds — electrical engineering, solid state physics, management, public policy, Asian studies, and career and international education. All members had strong track records and experience in international collaborations in research and education. At the core of this effort was the on-going collaboration between PI’s semiconductor spectroscopy group at Rice University and the crystal growth groups at Tokyo Institute of Technology and Osaka Institute of Technology, who are world leaders in the growth of 6.1 angstrom materials.
- Increased understanding of the quantum states and dynamics of interacting and/or strongly driven carriers in nanostructures
- Insight into the coherent and/or collective regime of exciton-light interaction
- Provision of a controlled environment in which to address unanswered questions in many-body physics
- Development of new device concepts and implementations based on 6.1 ˚Angstrom semiconductors.
- Increased students’ readiness for the fast-paced world of modern nanotechnology, new spectroscopy techniques, and novel device concepts and implementations.
- Our coupled research and education projects resulted in a greater long-term impact in the sciences.
- The combined education and research program endowed students (future researchers) with the skills necessary for a lifetime of international collaboration.
Our PIRE I grant for U.S.-Japan collaboration explores optical phenomena in semiconductors and carbon nanotubes grown by
our Japanese partners, using a variety of methods available in the laboratories of PI Kono and our Japanese partners. These experiments are coupled with theoretical studies by co-PIs Belyanin and Stanton. Two postdoctoral associates and 12 graduate students have been involved and trained in these projects (demographics for this group: three women, two African Americans, and one Hispanic American; six U.S. citizens, five Chinese citizens, two Indian citizens, and one Japanese citizen).
Below we describe five selected projects to highlight our successful activities in international research and education.
Accomplishment 1: Magnetic Brightening of “Dark” Excitons in Carbon Nanotubes
Single-walled carbon nanotubes (SWNTs) exhibit non-intuitive magnetic phenomena when threaded by a magnetic flux, arising from Aharonov-Bohm (AB) physics (1,2). Kono and Maruyama have collaborated to demonstrate the existence
of dark excitons in SWNTs by magnetically brightening them, (3-5) as a combined result of strong Coulomb
interactions and the AB effect (6-8). Kono and Yusa performed magneto-photoluminescence at mK temperatures, showing that a symmetry breaking effect brightens dark excitons without a magnetic field (9). These new effects are currently under study, in collaboration with Saito. Kono’s group also showed that SWNTs align in magnetic fields, and aligned SWNTs show strongly anisotropic optical properties (10-13). Kono and Imanaka have extended these studies to compare metallic and semiconducting SWNTs, (14) discovering that the magnetic susceptibility anisotropy of metallic tubes are one order of magnitude larger than that of semiconducting tubes.
Accomplishment 2: Ultrafast Optical Manipulation of Ferromagnetism
There has been much interest in optically controlling magnetization for spintronic-device development, and many studies have been performed on metallic and insulating ferromagnetic systems. (III,Mn)V ferromagnetic semiconductors are an ideal system for achieving this phenomenon, as Kono, Munekata, and Stanton have demonstrated (15-24). The carrierinduced nature of ferromagnetism in these systems naturally enables optical control of magnetism. Ultrashort laser pulses can create a large density of carriers, modifying the exchange interaction between Mn ions (20, 25, 26). Mittleman, Kono, and Munekata observed coherent THz radiation from laser-excited InMnAs, whose intensity and phase strongly changed with temperature (27). Furthermore, Kono and Munekata found that the agnetooptical Kerr angle for GaMnAs sensitively varies with the photon energy and temperature (28). Through comparison with 30-band k∙p calculations by Belyanin, they showed that the main spectral features can be understood as interband transitions,(29) without any ad hoc introduction of impurity transitions as reported by other groups.
SWNTs provide an ideal system for the exploration of novel one-dimensional (1-D) physics. Kono and collaborators have performed a series of ultrafast and nonlinear optical studies of SWNTs, elucidating the fundamental dynamical properties of 1-D carriers (30-32), phonons (33-37), and excitons (38-41). Kono, Lim, and Yee have observed coherent phonons (CPs) in SWNTs (33), which were used for simultaneously determining phonon and exciton energies. They have also developed a pulse-shaping method to specifically excite single-chirality SWNTs in samples containing SWNTs of many different chiralities (35). The excitation spectra of such selectively-excited CPs provided time-domain evidence that band gap oscillations follow the lattice oscillations. Sanders, Stanton, and Saito have developed a microscopic CP theory (35. 37), which correctly reproduced the overall trends in the observed chirality dependence of CP intensities.
Accomplishment 4: Thz Spectroscopy of Highly-aligned Carbon Nanotubes
Dynamic aspects of metallic SWNTs have been poorly explored, although novel effects are expected due to the exotic nature of interacting, 1-D electrons. Kono and Tonouchi have been studying the dynamic THz conductivity σ(ω) of metallic SWNTs.50 Many-body effects can affect the temperature and magnetic field dependence of σ(ω), sometimes in very specific ways, making this a useful method for comparing with theory. They have studied highly-aligned samples (see Fig. 3), ideal for polarization-dependent studies. Figure 3 (right) shows polarization dependent THz absorbance for θ = 0° to 90°, where θ is the angle between the nanotube axis and THz polarization.50 The absorbance monotonically decreases with increasing θ, and strikingly, is virtually absent when the THz polarization is perpendicular to the tube axis (θ = 90°).
Recognized by the Institute for International Education in 2008 as a ‘Best Practice in Study Abroad’ for expanding international research opportunities for U.S. engineering students (42), the NanoJapan Program annually involved 16 freshmen and sophomores in a 12-week International Research Experience for Undergraduates (IREU) program. Students spent three weeks in a language and culture orientation in Tokyo and then proceeded to their designated university lab where they conducted a nine week research internship in nanoscale science. Since the inaugural program in 2006 a total of 80 undergraduates have participated in NanoJapan. Of these students 33.8% were female and 8.9% were from underrepresented groups in Science, Technology, Engineering, and Math (STEM) fields. Participants have been selected from twenty-five colleges and universities throughout the U.S., including two students from community colleges. Of the 27 students who have graduated, 18 are currently enrolled in Master’s or Ph.D. programs in STEM fields and five student have been awarded prestigious, nationally-competitive fellowships for graduate study including the NSF Graduate Research Fellowships, Goldwater Fellowship, and Hertz Fellowship. Both of the community college participants are now enrolled in or applying to 4-year, B.S. programs.
1. J. Kono and S. Roche, “Magnetic Properties,” in: Carbon Nanotubes: Properties and Applications, edited by M. J. O’Connell (CRC Press, Taylor & Francis Group, Boca Raton, 2006), pp. 119- 151.
2. J. Kono, R. J. Nicholas, and S. Roche, “High Magnetic Field Phenomena in Carbon Nanotubes,” in: Carbon Nanotubes: Advanced Topics in the Synthesis, Structure, Properties and Applications, edited by A. Jorio, G. Dresselhaus, and M. S. Dresselhaus (Springer, Berlin, 2008), pp. 393 – 421.
3. J. Shaver, J. Kono, O. Portugall, V. Krsti, G. L. J. A. Rikken, Y. Miyauchi, S. Maruyama, and V. Perebeinos, “Magnetic Brightening of Carbon Nanotube Photoluminescence through Symmetry Breaking,” Nano Letters 7, 1851 (2007).
4. J. Shaver and J. Kono, ‘Temperature-Dependent Magneto-Photoluminescence Spectroscopy of Carbon Nanotubes: Evidence for Dark Excitons,’ Laser & Photonics Reviews 1, 260 (2007).
5. O. Portugall, V. Krstic, G. L. J. A. Rikken, J. Kono, J. Shaver, S. Zaric, V. C. Moore, R. H. Hauge, R. E. Smalley, Y. Miyauchi, and S. Maruyama, “Magneto spectroscopy of single-walled carbon nanotubes,” International Journal of Modern Physics B 21, 1189 (2007).
6. J. Shaver, S. A. Crooker, J. A. Fagan, E. K. Hobbie, N. Ubrig, O. Portugall, V. Perebeinos, P. Avouris, and J. Kono, “Magneto-optical Spectroscopy of Highly-Aligned Carbon Nanotubes: Identifying the Role of Threading Magnetic Flux,” Physical Review B 78, 081402(R) (2008).
7. A. Srivastava, H. Htoon, V. I. Klimov, and J. Kono, “Direct Observation of Dark Excitons in Individual Carbon Nanotubes: Inhomogeneity in the Exchange Splitting,” Physical Review Letters 101, 087402 (2008).
8. J. Shaver, A. Srivastava, J. Kono, S. A. Crooker, H. Htoon, V. I. Klimov, J. A. Fagan, E. K. Hobbie, N. Ubrig, O. Portugall, V. Perebeinos, and P. Avouris, “High-Field Magneto-Optical Spectroscopy of Highly-Aligned Individual and Ensemble Single-Walled Carbon Nanotubes,” International Journal of Modern Physics B 23, 2667 (2009).
9. L. G. Booshehri, S. Jong, T. A. Searles, G. Yusa, and J. Kono, “Nonlinear Magnetic Brightening and Non-thermal Distribution of Excitons in Carbon Nanotubes,” unpublished.
10. S. Zaric, G. N. Ostojic, J. Kono, J. Shaver, V. C. Moore, M. S. Strano, R. H. Hauge, R. E. Smalley, and X. Wei, “Optical Signatures of the Aharonov-Bohm Phase in Single-Walled Carbon Nanotubes,” Science 304, 1129 (2004).
11. S. Zaric, G. N. Ostojic, J. Kono, J. Shaver, V. C. Moore, R. H. Hauge, R. E. Smalley, and X. Wei, “Estimation of Magnetic Susceptibility Anisotropy of Carbon Nanotubes Using Magneto- Photoluminescence,” Nano Letters 4, 2219 (2004).
12. S. Zaric, G. N. Ostojic, J. Shaver, J. Kono, O. Portugall, P. H. Frings, G. L. J. A. Rikken, M. Furis, S. A. Crooker, X. Wei, R. H. Hauge, and R. E. Smalley, “Excitons in Carbon Nanotubes with Broken Time-Reversal Symmetry,” Physical Review Letters 96, 016406 (2006).
13. J. Shaver, A. N. G. Parra-Vasquez, S. Hansel, O. Portugall, C. H. Mielke, M. v. Ortenberg, R. H. Hauge, M. Pasquali, and J. Kono, “Alignment Dynamics of Carbon Nanotubes in Pulsed Ultrahigh Magnetic Fields,” ACS Nano 3, 131 (2009).
14. T. A. Searles, Y. Imanaka, J. A. Fagan, E. K. Hobbie, and J. Kono, “Large Magnetic Susceptibility Anisotropy of Metallic Single-Walled Carbon Nanotubes,” unpublished.
15. J. Wang, G. A. Khodaparast, J. Kono, T. Slupinski, A. Oiwa, and H. Munekata, “Ultrafast Optical Manipulation of Ferromagnetic Order in InMnAs/GaSb,” Journal of Superconductivity 16, 373 (2003).
16. G. A. Khodaparast, D. C. Larrabee, J. Kono, D. S. King, J. Kato, T. Slupinski, A. Oiwa, H. Munekata, G. D. Sanders, and C. J. Stanton, “Terahertz Dynamics of Photo-Generated Carriers in Ferromagnetic InGaMnAs,” Journal of Applied Physics 93, 8286 (2003).
17. J. Wang, J. Kono, A. Oiwa, H. Munekata, and C. J. Stanton, “Ultrafast Carrier Dynamics in Ferromagnetic InGaMnAs,” Superlattices and Microstructures34, 563 (2004).
18. J. Wang, G. A. Khodaparast, J. Kono, T. Slupinski, A. Oiwa, and H. Munekata, “Ultrafast Softening in InMnAs,” Physica E 20, 412 (2004).
19. J. Wang, G. A. Khodaparast, J. Kono, A. Oiwa, and H. Munekata, “Ultrafast Optical and Magneto-Optical Studies of Ferromagnetic III-V Semiconductors,” Journal of Modern Optics 51, 2771 (2004).
20. J. Wang, C. Sun, J. Kono, A. Oiwa, H. Munekata, Ł. Cywiński, and L. J. Sham, “Ultrafast Quenching of Ferromagnetism in InMnAs Induced by Intense Laser Irradiation,” Physical Review Letters 95, 167401 (2005).
21. J. Wang, Y. Hashimoto, J. Kono, A. Oiwa, H. Munekata, G. D. Sanders, and C. J. Stanton, “Propagating Coherent Acoustic Phonon Wave Packets in In1−xMnxAs/GaSb,” Physical Review B 72, 153311 (2005).
22. G. D. Sanders, C. J. Stanton, J. Wang, C. Sun, J. Kono, A. Oiwa, and H. Munekata, “Theory of Carrier Dynamics and Time-Resolved Reflectivity in InMnAs/GaSb Heterostructures,” Physical Review B 72, 245302 (2005).
23. J. Wang, C. Sun, Y. Hashimoto, J. Kono, G. A. Khodaparast, Ł. Cywiński, L. J. Sham, G. D. Sanders, C. J. Stanton, and H. Munekata, “Ultrafast Magneto-Optics in Ferromagnetic III-V Semiconductors,” Journal of Physics: Condensed Matter 18, R501 (2006).
24. J. Wang, Ł. Cywiński, C. Sun, J. Kono, H. Munekata, and L. J. Sham, “Femtosecond Demagnetization and and Hot-Hole Relaxation in Ferromagnetic Ga1-xMnxAs,” Physical Review B 77, 235 (2008).
25. J. Wang, C. Sun, Y. Hashimoto, J. Kono, G. A. Khodaparast, Ł. Cywiński, L. J. Sham, G. D. Sanders, C. J. Stanton, and H. Munekata, “Ultrafast Magneto-Optics in Ferromagnetic III-V Semiconductors,” Journal of Physics: Condensed Matter 18, R501 (2006).
26. J. Wang, Ł. Cywiński, C. Sun, J. Kono, H. Munekata, and L. J. Sham, “Femtosecond Demagnetization and Hot-Hole Relaxation in Ferromagnetic Ga1-xMnxAs,” Physical Review B 77, 235 (2008).
27. H. Zhan, J. Deibel, J. Laib, C. Sun, J. Kono, D. M. Mittleman, and H. Munekata, “Temperature Dependence of Terahertz Emission from InMnAs,” Applied Physics Letters 90, 012103 (2007).
28. H. Zhan, J. Deibel, J. Laib, C. Sun, J. Kono, D. M. Mittleman, and H. Munekata, “Temperature Dependence of Terahertz Emission from InMnAs,” Applied Physics Letters 90, 012103 (2007).
29. C. Sun, J. Kono, Y. Cho, A. K. Wójcik, A. Belyanin, and H. Munekata, “Magneto-optical Kerr Spectroscopy of GaMnAs: Interband or Impurity Transitions?,” Physical Review Letters, under review (arXiv:0907.1546v1).
30. J. Kono, G. N. Ostojic, S. Zaric, M. S. Strano, V. C. Moore, J. Shaver, R. H. Hauge, and R. E. Smalley, “Ultrafast Optical Spectroscopy of Micelle-Suspended Single-Walled Carbon Nanotubes,” Applied Physics A 78, 1093 (2004).
31. G. N. Ostojic, S. Zaric, J. Kono, M. S. Strano, V. C. Moore, R. H. Hauge, and R. E. Smalley, “Interband Recombination Dynamics of Resonantly-Excited Single-Walled Carbon Nanotubes,” Physical Review Letters 92, 117402 (2004).
32. Y. Hashimoto, Y. Murakami, S. Maruyama, and J. Kono, “Anisotropic Decay Dynamics of Photoexcited Aligned Carbon Nanotube Bundles,” Physical Review B 75, 245408 (2007).
33. Y.-S. Lim, K.-J. Yee, J.-H. Kim, E. H. Hároz, J. Shaver, J. Kono, S. K. Doorn, R. H. Hauge, and R. E. Smalley, “Coherent Lattice Vibrations in Single-Walled Carbon Nanotubes,” Nano Letters 6, 26 (2006).
34. Y.-S. Lim, K.-J. Yee, J.-H. Kim, E. H. Hároz, J. Shaver, J. Kono, S. K. Doorn, R. H. Hauge, and R. E. Smalley, “Chirality Assignment of Micelle-Suspended Single-Walled Carbon Nanotubes Using Coherent Phonon Oscillations,” Journal of Korean Physical Society 51, 306 (2007).
35. J.-H. Kim, K.-J. Han, N.-J. Kim, K.-J. Yee, Y.-S. Lim, G. D. Sanders, C. J. Stanton, L. G. Booshehri, E. H. Hároz, and J. Kono, “Chirality-Selective Excitations of Coherent Phonons in Carbon Nanotubes by Femtosecond Optical Pulses,” Physical Review Letters 102, 037402 (2009).
36. J.-H. Kim, J.-G. Park, B.-Y. Lee, D.-H. Lee, K.-J. Yee, Y.-S. Lim, L. G. Booshehri, E. H. Hároz, J. Kono, and S.-H. Baik, “Polarization Anisotropy of Transient Carrier and Phonon Dynamics in Carbon Nanotubes,” Journal of Applied Physics 105, 103506 (2009).
37. G. D. Sanders, C. J. Stanton, J.-H. Kim, K.-J. Yee, Y.-S. Lim, E. H. Hároz, L. G. Booshehri, J. Kono, and R. Saito, “Resonant Coherent Phonon Spectroscopy of Single-Walled Carbon Nanotubes,” Physical Review B 79, 205 (2009).
38. G. N. Ostojic, S. Zaric, J. Kono, V. C. Moore, R. H. Hauge, and R. E. Smalley, “Stability of High- Density One-Dimensional Excitons in Carbon Nanotubes under High Laser Excitation,” Physical Review Letters 94, 097401 (2005).
39. Y. Murakami and J. Kono, “Nonlinear Photoluminescence Excitation Spectroscopy of Carbon Nanotubes: Exploring the Upper Density Limit of One-Dimensional Excitons,” Physical Review Letters 102, 037401 (2009).
40. A. Srivastava and J. Kono, “Diffusion-Limited Exciton-Exciton Annihilation in Single-Walled Carbon Nanotubes: A Time-Dependent Analysis,” Physical Review B 79, 205407 (2009).
41. Y. Murakami and J. Kono, “Existence of an Upper Limit on the Density of Excitons in Carbon Nanotubes by Diffusion-Limited Exciton-Exciton Annihilation: Experiment and Theory,” Physical Review B 80, 035432 (2009).
42. 2008 Institute of International Education Heiskell Award: ‘Best Practice in Study Abroad’ for providing an innovative program that makes study abroad more accessible to a broader student population. To learn more see http://www.iienetwork.org/page/117769/.