Browsing by Author "Kono, J."
Now showing 1 - 20 of 22
Results Per Page
Sort Options
Item Circular polarization dependent cyclotron resonance in large-area graphene in ultrahigh magnetic fields(American Physical Society, 2012) Booshehri, L.G.; Mielke, C.H.; Rickel, D.G.; Crooker, S.A.; Zhang, Q.; Ren, L.; Haroz, E.H.; Rustagi, A.; Stanton, C.J.; Jin, Z.; Sun, Z.; Yan, Z.; Tour, J.M.; Kono, J.Using ultrahigh magnetic fields up to 170 T and polarized midinfrared radiation with tunable wavelengths from 9.22 to 10.67 μm, we studied cyclotron resonance in large-area graphene grown by chemical vapor deposition. Circular polarization dependent studies reveal strong p-type doping for as-grown graphene, and the dependence of the cyclotron resonance on radiation wavelength allows for a determination of the Fermi energy. Thermal annealing shifts the Fermi energy to near the Dirac point, resulting in the simultaneous appearance of hole and electron cyclotron resonance in the magnetic quantum limit, even though the sample is still p-type, due to graphene's linear dispersion and unique Landau level structure. These high-field studies therefore allow for a clear identification of cyclotron resonance features in large-area, low-mobility graphene samples.Item Collective antenna effects in the terahertz and infrared response of highly aligned carbon nanotube arrays(The American Physical Society, 2013) Ren, L.; Zhang, Q.; Pint, C.L.; Wójcik, A.K.; Bunney, M. Jr; Arikawa, T.; Kawayama, I.; Tonouchi, M.; Hauge, R.H.; Belyanin, A.A.; Kono, J.We study macroscopically aligned single-wall carbon nanotube arrays with uniform lengths via polarization-dependent terahertz and infrared transmission spectroscopy. Polarization anisotropy is extreme at frequencies less than ∼100 cm−1 with no sign of attenuation when the polarization is perpendicular to the alignment direction. The attenuation for both parallel and perpendicular polarizations increases with increasing frequency, exhibiting a pronounced and broad peak around 450 cm−1 in the parallel case. We model the electromagnetic response of the sample by taking into account both radiative scattering and absorption losses. We show that our sample acts as an effective antenna due to the high degree of alignment, exhibiting much larger radiative scattering than absorption in the mid/far-infrared range. Our calculated attenuation spectrum clearly shows a non-Drude peak at ∼450 cm−1 in agreement with the experiment.Item Dephasing of G-band phonons in single-wall carbon nanotubes probed via impulsive stimulated Raman scattering(American Physical Society, 2012) Kim, J.-H.; Yee, K.-J.; Lim, Y.-S.; Booshehri, L.G.; Haroz, E.H.; Kono, J.We study the coherent dynamics of G-band phonons in single-wall carbon nanotubes through impulsive stimulated Stokes and anti-Stokes Raman scattering. The probe energy dependence of the phonon amplitude as well as the preferential occurrence between Stokes and anti-Stokes components in response to chirpedpulse excitation are well explained within our model. The temperature dependence of the observed dephasing rate clearly exhibits a thermally activated component, with an activation energy that coincides with the frequency of the radial breathing mode (RBM). This fact provides a clear picture for the dephasing of G-band phonons by random frequency modulation via interaction with the RBM through anharmonicity.Item Effects of electron-electron interactions on the electronic Raman scattering of graphite in high magnetic fields(American Physical Society, 2014) Ma, Y.; Kim, Y.; Kalugin, N.G.; Lombardo, A.; Ferrari, A.C.; Kono, J.; Imambekov, A.; Smirnov, D.We report the observation of strongly temperature (T)-dependent spectral lines in electronic Raman-scattering spectra of graphite in a high magnetic field up to 45 T applied along the c axis. The magnetic field quantizes the in-plane motion, while the out-of-plane motion remains free, effectively reducing the system dimension from 3 to 1. Optically created electron-hole pairs interact with, or shake up, the one-dimensional Fermi sea in the lowest Landau subbands. Based on the Tomonaga-Luttinger liquid theory, we show that interaction effects modify the spectral line shape from (ω−Δ)−1/2 to (ω−Δ)2α−1/2 at T = 0. At finite T, we predict a thermal broadening factor that increases linearly with T. Our model reproduces the observed T-dependent line shape, determining the electron-electron interaction parameter α to be ∼0.05 at 40 T.Item Effects of etchants in the transfer of chemical vapor deposited graphene(AIP, 2018) Wang, M.; Yang, E.H.; Vajtai, R.; Kono, J.; Ajayan, P.M.The quality of graphene can be strongly modified during the transfer process following chemical vapor deposition (CVD) growth. Here, we transferred CVD-grown graphene from a copper foil to a SiO2/Si substrate using wet etching with four different etchants: HNO3, FeCl3, (NH4)2S2O8, and a commercial copper etchant. We then compared the quality of graphene after the transfer process in terms of surface modifications, pollutions (residues and contaminations), and electrical properties (mobility and density). Our tests and analyses showed that the commercial copper etchant provides the best structural integrity, the least amount of residues, and the smallest doping carrier concentration.Item Flexible and stackable terahertz metamaterials via silver-nanoparticle inkjet printing(AIP Publishing, 2018) Kashiwagi, K.; Xie, L.; Li, X.; Kageyama, T.; Miura, M.; Miyashita, H.; Kono, J.; Lee, S.-S.There is presently much interest in tunable, flexible, or reconfigurable metamaterial structures that work in the terahertz frequency range. They can be useful for a range of applications, including spectroscopy, sensing, imaging, and communications. Various methods based on microelectromechanical systems have been used for fabricating terahertz metamaterials, but they typically require high-cost facilities and involve a number of time-consuming and intricate processes. Here, we demonstrate a simple, robust, and cost-effective method for fabricating flexible and stackable multiresonant terahertz metamaterials, using silver nanoparticle inkjet printing. Using this method, we designed and fabricated two arrays of split-ring resonators (SRRs) having different resonant frequencies on separate sheets of paper and then combined the two arrays by stacking. Through terahertz time-domain spectroscopy, we observed resonances at the frequencies expected for the individual SRR arrays as well as at a new frequency due to coupling between the two SRR arrays.Item Imaging molecular adsorption and desorption dynamics on graphene using terahertz emission spectroscopy(Nature Publishing Group, 2014) Ajayan, P.M.; Kono, J.; Tonouchi, M.Being an atomically thin material, graphene is known to be extremely susceptible to its environment, including defects and phonons in the substrate on which it is placed as well as gas molecules that surround it. Thus, any device design using graphene has to take into consideration all surrounding components, and device performance needs to be evaluated in terms of environmental influence. However, no methods have been established to date to readily measure the density and distribution of external perturbations in a quantitative and non-destructive manner. Here, we present a rapid and non-contact method for visualizing the distribution of molecular adsorbates on graphene semi-quantitatively using terahertz time-domain spectroscopy and imaging. We found that the waveform of terahertz bursts emitted from graphene-coated InP sensitively changes with the type of atmospheric gas, laser irradiation time, and ultraviolet light illumination. The terahertz waveform change is explained through band structure modifications in the InP surface depletion layer due to the presence of localized electric dipoles induced by adsorbed oxygen. These results demonstrate that terahertz emission serves as a local probe for monitoring adsorption and desorption processes on graphene films and devices, suggesting a novel two-dimensional sensor for detecting local chemical reactions.Item Impact of growth temperature on InAs/GaInSb strained layer superlattices for very long wavelength infrared detection(American Institute of Physics, 2012-10-23) Haugan, H.J.; Brown, G.J.; Elhamri, S.; Mitchel, W.C.; Mahalingam, K.; Kim, M.; Noe, G.T.; Ogden, N.E.; Kono, J.We explore the optimum growth space for a 47.0A ° InAs/21.5A ° Ga0.75In0.25Sb superlattices (SLs) designed for the maximum Auger suppression for a very long wavelength infrared gap. Our growth process produces a consistent gap of 5065meV. However, SL quality is sensitive to the growth temperature (Tg). For the SLs grown at 390 470 C, a photoresponse signal gradually increases as Tg increases from 400 to 440 C. Outside this temperature window, the SL quality deteriorates very rapidly. All SLs were n-type with mobility of 10 000 V/cm2 and 300K recombination lifetime of 70 ns for an optimized SLItem Impact on Student Learning: A Comparison of International and Domestic Undergraduate Research Experiences(2014) Matherly, C.A.; Phillips, S.R.; Kono, J.; NanoJapanItem Magnetooptics of Exciton Rydberg States in a Monolayer Semiconductor(American Physical Society, 2018) Stier, A.V.; Wilson, N.P.; Velizhanin, K.A.; Kono, J.; Xu, X.; Crooker, S.A.We report 65 T magnetoabsorption spectroscopy of exciton Rydberg states in the archetypal monolayer semiconductor WSe2. The strongly field-dependent and distinct energy shifts of the 2s, 3s, and 4s excited neutral excitons permits their unambiguous identification and allows for quantitative comparison with leading theoretical models. Both the sizes (via low-field diamagnetic shifts) and the energies of the ns exciton states agree remarkably well with detailed numerical simulations using the nonhydrogenic screened Keldysh potential for 2D semiconductors. Moreover, at the highest magnetic fields, the nearly linear diamagnetic shifts of the weakly bound 3s and 4s excitons provide a direct experimental measure of the exciton’s reduced mass mr=0.20±0.01m0.Item Magnetotransport in type-enriched single-wall carbon nanotube networks(American Physical Society, 2018) Wang, X.; Gao, W.; Li, X.; Zhang, Q.; Nanot, S.; Hároz, E.H.; Kono, J.; Rice, W.D.Single-wall carbon nanotubes (SWCNTs) exhibit a wide range of physical phenomena depending on their chirality. Nanotube networks typically contain a broad mixture of chiralities, which prevents an in-depth understanding of SWCNT ensemble properties. In particular, electronic-type mixing (the simultaneous presence of semiconductor and metallic nanotubes) in SWCNT networks remains the single largest hurdle to developing a comprehensive view of ensemble nanotube electrical transport, a critical step toward their use in optoelectronics. Here, we systematically study temperature-dependent magnetoconductivity (MC) in networks of highly enriched semiconductor and metal SWCNT films. In the semiconductor-enriched network, we observe two-dimensional variable-range hopping conduction from 5 to 290 K. Low-temperature MC measurements reveal a large, negative MC from which we determine the wave-function localization length and Fermi energy density of states. In contrast, the metal-enriched film exhibits positive MC that increases with decreasing temperature, a behavior attributed to two-dimensional weak localization. Using this model, we determine the details of the carrier phase coherence and fit the temperature-dependent conductivity. These extensive measurements on type-enriched SWCNT networks provide insights that pave the way for the use of SWCNTs in solid-state devices.Item Measurement of Filling-Factor-Dependent Magnetophonon Resonances in Graphene Using Raman Spectroscopy(American Physical Society, 2013-05-29) Kim, Y.; Poumirol, J.M.; Lombardo, A.; Kalugin, N.G.; Georgiou, T.; Kim, Y.J.; Novoselov, K.S.; Ferrari, A.C.; Kono, J.; Kashuba, O.; Fal’ko, V.I.; Smirnov, D.We perform polarization-resolved Raman spectroscopy on graphene in magnetic fields up to 45 T. This reveals a filling-factor-dependent, multicomponent anticrossing structure of the Raman G peak, resulting from magnetophonon resonances between magnetoexcitons and E2g phonons. This is explained with a model of Raman scattering taking into account the effects of spatially inhomogeneous carrier densities and strain. Random fluctuations of strain-induced pseudomagnetic fields lead to increased scattering intensity inside the anticrossing gap, consistent with the experiments.Item Midinfrared third-harmonic generation from macroscopically aligned ultralong single-wall carbon nanotubes(American Physical Society, 2013) Morris, D.T.; Pint, C.L.; Arvidson, R.S.; Luttge, A.; Hauge, R.H.; Belyanin, A.A.; Woods, G.L.; Kono, J.We report the observation of strong third-harmonic generation from a macroscopic array of aligned ultralong single-wall carbon nanotubes (SWCNTs)with intensemidinfrared radiation. Through power-dependent experiments, we determined the absolute value of the third-order nonlinear optical susceptibility !(3) of our SWCNT film to be 5.53 × 10−12 esu, three orders of magnitude larger than that of the fused silica reference we used. Taking account of the filling factor of 8.75% for our SWCNT film, we estimate a !(3) of 6.32 × 10−11 esu for a fully dense film. Furthermore, through polarization-dependent experiments, we extracted all the nonzero elements of the !(3) tensor, determining the magnitude of the weaker tensor elements to be #1/6 of that of the dominant !(3) zzzz component.Item NanoJapan International Research Experience for Undergraduates: Preparing Globally Engaged Science and Engineers(2013) Matherly, C.A.; Phillips, S.R.; Kono, J.; NanoJapanThe NanoJapan: International Research Experience for Undergraduates Program, established by a National Science Foundation Partnerships for International Research and Education (NSF-PIRE) grant in 2006, is a twelve-week summer program through which twelve freshman and sophomore physics and engineering students from U.S. universities complete research internships in Japanese nanotechnology laboratories. NanoJapan tightly integrates the international experience with students’ academic programs by providing hands-on opportunities to acquire technical skills and knowledge associated with cutting-edge nanotechnology research projects. The program aims to increase the numbers of U.S. students who pursue graduate study in nanoscience and cultivate a generation of globally aware engineers and scientists who are prepared for international research collaboration. The NanoJapan program is the key educational initiative of the National Science Foundation–funded Partnerships for International Research and Education (NSF-PIRE) grant awarded to the Electrical and Computer Engineering Department of Rice University and the Center for Global Education at the University of Tulsa. The program was awarded five years of funding in 2006 and has been renewed for another five years. This paper will provide an overview and justification for the development of the NanoJapan Program, provide an overview of our program assessment and student outcomes to date, and conclude with an overview of the potential impact of the NanoJapan Program model on STEM education and international engineering programs nationwide.Item NanoJapan-International research experience for undergraduates program: Fostering U.S.-Japan research collaborations in terahertz science and technology of nanostructures(SPIE, 2014-09-15) Phillips, S.R.; Matherly, C.A.; Kono, J.; NanoJapanThe international nature of science and engineering research demands that students have the skillsets necessary to collaborate internationally. However, limited options exist for science and engineering undergraduates who want to pursue research abroad. The NanoJapan International Research Experience for Undergraduates Program is an innovative response to this need. Developed to foster research and international engagement among young undergraduate students, it is funded by a National Science Foundation Partnerships for International Research and Education (PIRE) grant. Each summer, NanoJapan sends 12 U.S. students to Japan to conduct research internships with world leaders in terahertz (THz) spectroscopy, nanophotonics, and ultrafast optics. The students participate in cutting-edge research projects managed within the framework of the U.S-Japan NSF-PIRE collaboration. One of our focus topics is THz science and technology of nanosystems (or ‘TeraNano’), which investigates the physics and applications of THz dynamics of carriers and phonons in nanostructures and nanomaterials. In this article, we will introduce the program model, with specific emphasis on designing high-quality international student research experiences. We will specifically address the program curriculum that introduces students to THz research, Japanese language, and intercultural communications, in preparation for work in their labs. Ultimately, the program aims to increase the number of U.S. students who choose to pursue graduate study in this field, while cultivating a generation of globally aware engineers and scientists who are prepared for international research collaboration.Item NanoJapan: Connecting U.S. Undergraduates with the Best of Nanoscience Research in Japan(2011) Matherly, C.A.; Phillips, S.R.; Kono, J.; NanoJapanItem Observation of Forbidden Exciton Transitions Mediated by Coulomb Interactions in Photoexcited Semiconductor Quantum Wells(American Physical Society, 2013) Rice, W.D.; Kono, J.; Zybell, S.; Winnerl, S.; Bhattacharyya, J.; Schneider, H.; Helm, M.; Ewers, B.; Chernikov, A.; Koch, M.; Chatterjee, S.; Khitrova, G.; Gibbs, H.M.; Schneebeli, L.; Breddermann, B.; Kira, M.; Koch, S.W.We use terahertz pulses to induce resonant transitions between the eigenstates of optically generated exciton populations in a high-quality semiconductor quantum well sample. Monitoring the excitonic photoluminescence, we observe transient quenching of the 1s exciton emission, which we attribute to the terahertz-induced 1s-to-2p excitation. Simultaneously, a pronounced enhancement of the 2s exciton emission is observed, despite the 1s-to-2s transition being dipole forbidden. A microscopic many-body theory explains the experimental observations as a Coulomb-scattering mixing of the 2s and 2p states, yielding an effective terahertz transition between the 1s and 2s populations.Item Renormalized energies of superfluorescent bursts from an electron-hole magnetoplasma with high gain in InxGa1−xAs quantum wells(American Physical Society, 2013) Kim, J.-H.; Lee, J.; Noe, G.T.; Wang, Y.; Wojcik, A.K.; McGill, S.A.; Reitze, D.H.; Belyanin, A.A.; Kono, J.We study light emission properties of a population-inverted 2D electron-hole plasma in a quantizing magnetic field. We observe a series of superfluorescent (SF) bursts, discrete both in time and energy, corresponding to the cooperative recombination of electron-hole pairs from different Landau levels. Emission energies exhibit strong renormalization due to many-body interactions among the photogenerated carriers, showing pronounced red shifts as large as 20 meV at 15 T. However, the lowest Landau level emission line remains stable against renormalization and show excitonic magnetic field dependence. Interestingly, our time-resolved measurements show that this lowest-energy SF burst occurs only after most upper states become empty, suggesting that this excitonic stability is related to the “hidden symmetry” of 2D magnetoexcitons expected in the magnetic quantum Limit.Item Rice University NanoJapan Program: Connecting US Undergraduates with Leading Japanese Nanotechnology Research Laboratories: National Science Foundation, Tokyo Regional Office(2008-04-17) Kono, J.; Phillips, S.R.; Matherly, C.A.; NanoJapanNational Science Foundation, Tokyo Regional Office: Special Scientific Report #08-01. As international partnerships are becoming increasingly indispensible to solving major science and engineering problems, U.S. researchers and educators must be able to operate effectively in teams comprised of partners from different nations and cultural backgrounds. The NanoJapan Program was developed to address this need by attracting undergraduate students to the emerging areas of electrical engineering and the physical sciences, especially the study of nanotechnology. By involving and training students in cutting-edge research projects in nanoscale science and engineering, this program aims to increase the numbers of US students who choose to pursue graduate study in this field while also cultivating a generation of globally aware engineers and scientists who are prepared for international research collaboration. Funded by a Partnership for International Research and Education grant from the National Science Foundation (NSF-PIRE), this program is administered through the Electrical and Computer Engineering Department of Rice University and the Center for Global Education at the University of Tulsa.Item Scaling law for excitons in 2D perovskite quantum wells(Springer Nature, 2018) Blancon, J.-C.; Stier, A.V.; Tsai, H.; Nie, W.; Stoumpos, C.C.; Traoré, B.; Pedesseau, L.; Kepenekian, M.; Katsutani, F.; Noe, G.T.; Kono, J.; Tretiak, S.; Crooker, S.A.; Katan, C.; Kanatzidis, M.G.; Crochet, J.J.; Even, J.; Mohite, A.D.Ruddlesden-Popper halide perovskites are 2D solution-processed quantum wells with a general formula A2A'n-1M n X3n+1, where optoelectronic properties can be tuned by varying the perovskite layer thickness (n-value), and have recently emerged as efficient semiconductors with technologically relevant stability. However, fundamental questions concerning the nature of optical resonances (excitons or free carriers) and the exciton reduced mass, and their scaling with quantum well thickness, which are critical for designing efficient optoelectronic devices, remain unresolved. Here, using optical spectroscopy and 60-Tesla magneto-absorption supported by modeling, we unambiguously demonstrate that the optical resonances arise from tightly bound excitons with both exciton reduced masses and binding energies decreasing, respectively, from 0.221 m0 to 0.186 m0 and from 470 meV to 125 meV with increasing thickness from n equals 1 to 5. Based on this study we propose a general scaling law to determine the binding energy of excitons in perovskite quantum wells of any layer thickness.