Here we propose that hybrid heterostructures, composed of inorganic nanostructures grown directly on 2-dimentional layered materials such as graphene, are the most promising material system for flexible device applications. In particular, the hybrid heterostructures composed of high-quality GaN thin films or nanostructures grown directly on graphene offer a novel material system for transferable and/or flexible optoelectronics. The inorganic nanostructures in the hybrid nanomaterials exhibit excellent electrical and optical characteristics, including high carrier mobility, radiative recombination rate, and long-term stability. Meanwhile, for the flexible devices based on the hybrid structures, the graphene layers, which have excellent electrical and thermal conductivity, high mechanical strength and elasticity, and/or optical transparency, act as a novel substrate offering new functionalities such as transferability or flexibility. Here I will present on position- and morphology-controlled growths of ZnO nanostructures using catalyst-free metal-organic vapor phase epitaxy and describe the methods to fabricate flexible LEDs based on nitride coated ZnO nanostructures grown on graphene, which exhibit strong light emission after the transfer onto foreign substrates, such as metal, glass, and plastic. We believe that our unique technology to make hybrid nanomaterials will make paradigm shift from rigid to flexible and planar to three-dimensional inorganic semiconductor structures and devices.
Electrocorticography (ECoG) is a powerful tool for direct mapping of local field potentials from the brain surface. Progress in development of high-fidelity materials such as poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) on thin conformal substrates such as parylene C enabled intimate contact with cortical surfaces and higher quality recordings from small volumes of neurons. Meanwhile, stimulation of neuronal activity is conventionally accomplished with electrical microstimulation and transcranial magnetic stimulation that can be combined with ECoG to form the basis of bidirectional neural interface. However, these stimulation mechanisms are less controlled and primitively understood on the local and cellular levels. With the advent of optogenetics, the localization and specificity of neuronal stimulation and inhibition is possible. Therefore, the development of integrated devices that can merge the sensitivity of ECoG or depth recording with optogenetic tools can lead to newer frontiers in understanding the neuronal activity.
Herein, we introduce a hybrid device comprising flexible inorganic LED arrays integrated PEDOT:PSS/parylene C microelectrode arrays for high resolution bidirectional neuronal interfaces. The flexible inorganic LEDs have been developed by the metal-organic vapor phase epitaxy of position-controlled GaN microLEDs on ZnO nanostructured templates pre-grown at precise locations on a graphene layer. By transferring it onto the microelectrode arrays, it can provides the individual electrical addressability by light stimulation patterns. We will present experimental and simulation results on the optoelectronic characteristics and light activation capability of flexible microLEDs and their evaluation in vivo.
Zinc blende ZnSe longitudinal twinning nanowires (Type I) and a sandwich structure with the wurtzite ZnSe inserting into the zinc blende ZnSe longitudinal twinning nanowires (Type II) are fabricated via a simple thermal evaporation method. The growth of them might be caused by the crystal plane slip during the phase transformation process from wurtzite ZnSe to zinc blende ZnSe nanowire. The wurtzite ZnSe might have two origins: 1) The phase transformed wurtzite from zinc blende. At first, during the temperature rising stage in the experiment, before the temperature approached to the transformation temperature (Ttr), ZnSe in zinc blende phase might begin to nucleate and grow. Once the temperature is higher than Ttr, the zinc blende products would transform to wurtzite phase. 2) The new-born nuclei grown wurtzite phase at high temperature for it is reported that the wurtzite phase is more stable at higher temperature. During the cooling period, the source material is exhausted and no more nucleation would occur. Some of the wurtzite products would transform to zinc blende phase when the temperature is lower than Ttr. During the process, it is reasonable that the ZB phase begins to form from the outer sides of an individual nanowire. Once the process completes, the longitudinal twinning ZB nanowire would be obtained; otherwise, the sandwich-structured nanowire forms.
This proceeding summarizes the materials preparation of position-controlled ZnO-based nanorod heterostructures and
fabrication of vertically-aligned wide band gap semiconductor nanorod light-emitting devices. Especially the fabrication
of GaN/InxGa1-xN/GaN/ZnO nanorod heterostructured visible-light-emitter arrays on sapphire and Si substrates,
representing important progress in the field of nanoheteroepitaxy and photonic devices in nanoscale, are reported.
Particularly, position-controlled vertical nanostructure arrays make those possible to prepare high-quality material
systems without stress or strain accumulation and to fabricate high-performance light-emitting devices (LEDs) with a
three-dimensional device configuration. Our method based on nanoheteroepitaxy and position-controlled nanodevice
integration for fabricating GaN-based micro-LED arrays constitutes a promising strategy for resolving the issues of
conventional GaN LEDs and fabricating high-performance LEDs on various substrates for potential optoelectronic
integrated circuits and solid-state lighting applications.
A dual-beam method for the near-axial rotation of dielectric nanorods was devised. The method uses two laser beams, where a focused Gaussian beam holds the object in the beam axis while a focused Laguerre-Gaussian beam rotates the object. The near-axial rotation of ZnO nanorods using this method was then experimentally demonstrated, and the radial offset distance of the rotating nanorod from the beam axis was quantified via a video tracking method.
Optical trapping of nanorods has attracted many researchers due to many potential applications of nanorods in sensor
technologies. It is well known that nanorods align with the propagation axis or the polarization direction of a laser beam.
However, there are only few studies about the axial rotation of nanorods. In this study, we present a method for the
measurement of the rotational frequency of nanorods.
KEYWORDS: Near field, Zinc oxide, Excitons, Quantum wells, Nanophotonics, Near field optics, Energy transfer, Time resolved spectroscopy, Picosecond phenomena, Nanorods
We review recent progress in the development of nanophotonic devices using the optical near-field interaction. ZnO
nanocrystallites are potentially ideal components for realizing room-temperature operation of such devices due to their
high exciton-binding energy and great oscillator strength. To confirm this promising optical property of ZnO, we
examined the near-field time-resolved spectroscopy of ZnO nanorod double-quantum-well structures (DQWs). First, we
observed the nutation of the population between the resonantly coupled exciton states of DQWs, in which the coupling
strength of the near-field interaction was found to decrease exponentially as the separation increased. Furthermore, we
successfully demonstrated the AND-gate operation by controlling a dipole-forbidden optical energy transfer among
resonant exciton states. Our results provide criteria for designing nanophotonic devices. The success of time-resolved
near-field spectroscopy of isolated DQWs described here is a promising step toward realizing a practical nanometerscale
photonic switch and related devices.
KEYWORDS: Quantum wells, Zinc oxide, Near field, Nanophotonics, Excitons, Near field optics, Switching, Energy transfer, Picosecond phenomena, Nanorods
We review recent progress in the development of nanophotonic devices using the optical near-field interaction. ZnO nanocrystallites are potentially ideal components for realizing room-temperature operation of such devices due to their high exciton-binding energy and great oscillator strength. To confirm this promising optical property of ZnO, we examined the near-field time-resolved spectroscopy of ZnO nanorod double-quantum-well structures (DQWs). First, we
observed the nutation of the population between the resonantly coupled exciton states of DQWs, in which the coupling
strength of the near-field interaction was found to decrease exponentially as the separation increased. Furthermore, we
successfully demonstrated the switching dynamics of a
dipole-forbidden optical energy transfer among resonant exciton
states. Our results provide criteria for designing nanophotonic devices. The success of time-resolved near-field
spectroscopy of isolated DQWs described here is a promising step toward realizing a practical nanometer-scale photonic
switch and related devices.
We report on fabrications and characteristics of high performance ZnO nanorod nanodevices including Schottky diodes, metal-oxide-semiconductor field-effect transistors (MOSFETs), metal-semiconductor field-effect transistors (MESFETs) and logic gate devices. Electrical characteristics of several ZnO nanorod MOSFETs are compared in this proceeding. In particular, after coating polymer thin films on ZnO nanorod surfaces, the nanorod MOSFETs exhibited much improved field effect transistor characteristics including field effect electron mobility as high as 3000 cm2/Vs. In addition, ZnO nanorod Schottky diodes and MESFETs were fabricated using Au/ZnO Schottky contacts without any specific oxide etching process. These devices have been used for realization of ZnO nanorod logic gates.
We report on catalyst-free growth of ZnO nanorods and their nano-scale electrical and optical device applications. Catalyst-free metalorganic vapor-phase epitaxy (MOVPE) enables fabrication of size-controlled high purity ZnO single crystal nanorods. Various high quality nanorod heterostructures and quantum structures based on ZnO nanorods were also prepared using the MOVPE method and characterized using scanning electron microscopy, transmission electron microscopy, and optical spectroscopy. From the photoluminescence spectra of ZnO/Zn0.8Mg0.2O nanorod multi-quantum-well structures, in particular, we observed a systematic blue-shift in their PL peak position due to quantum confinement effect of carriers in nanorod quantum structures. For ZnO/ZnMgO coaxial nanorod heterostructures, photoluminescence intensity was significantly increased presumably due to surface passivation and carrier confinement. In addition to the growth and characterizations of ZnO nanorods and their quantum structures, we fabricated nanoscale electronic devices based on ZnO nanorods. We report on fabrication and device characteristics of metal-oxidesemiconductor field effect transistors (MOSFETs), Schottky diodes, and metal-semiconductor field effect transistors (MESFETs) as examples of the nanodevices. In addition, electroluminescent devices were fabricated using vertically aligned ZnO nanorods grown p-type GaN substrates, exhibiting strong visible electroluminescence.
We report on photoluminescent properties of ultrafine ZnO nanorods and ZnO/Zn0.8Mg0.2O nanorod quantum-well structures. The catalyst-free metalorganic chemical vapor deposition (MOCVD) technique enables control of ZnO nanorod diameters in the range of 5 to 150 nm. From the PL spectra of ultrafine ZnO nanorods with a mean diameter smaller than 10 nm, a systematic blue-shift in their PL peak position was observed by decreasing their diameter, presumably due to the quantum confinement effect along the radial direction in ZnO nanorods. In addition, we obtained time-integrated and time-resolved PL spectra of ZnO/Zn0.8Mg0.2O nanorod single-quantum-well structures (SQWs) in the temperature range of 10 K to 300 K. The nanorod SQWs also showed a PL blue-shift and the energy shift was dependent on ZnO well layer width. The PL peak position shift originates from the quantum confinement effect of carriers in nanorod quantum structures. Furthermore, we investigated spatially-resolved PL spectra of individual nanorod SQWs using scanning near-field optical microscopy.
The dynamics of the bound and free excitons and exiton polaritons of the ZnO nanorods have been investigated by time resolved photoluminescence in the temperature range from 10 K to 300 K. The samples have been fabricated by catalyst-free metal organic chemical vapor deposition (MOCVD), and have a diameter 35 nm and lengths in the range of 150 nm to 1.1 μm. In the temperature range of 10 K to 50 K, the photoluminescence lifetime of the bound exciton increases as the temperature increases. Photoluminescence lifetime of the free excitons, however, decreases with the temperature. The low temperature (10 K) time resolved photoluminescence spectra reconstructed from the time profiles measured at different frequencies clearly show that the bound exciton decay faster than the free A exciton. This result may be due to the transition from the bound exciton to free exciton because of the local temperature increase. Free B exciton is dominant above 50 K, and forms exciton polariton at high temperatures. At low temperature, photoluminescence lifetimes of the free A and B excitons do not show a clear correlation with the length of the nanorods. At room temperature, however, the photoluminescence lifetime increases monotonically as the length of the nanorods increase in the range of 150 nm to 600 nm. Decrease of the radiative decay rate of the exciton polariton has been invoked to account for the results.
We report on photoluminescence (PL) properties of ZnO epitaxial films and single-crystal nanorods grown by low pressure metalorganic vapor phase epitaxy. Time-integrated PL spectra of the films at 10 K clearly exhibited free A and B excitons at 3.376 and 3.382 eV and bound exciton peaks at 3.360, 3.364, and 3.367 eV. With increasing temperature, intensities of the bound exciton peaks drastically decreased and a free exciton peak was dominant above 40 K. Similarly, vertically well-aligned ZnO nanorod arrays also exhibited free exciton peaks at 3.374 and 3.381 eV, which indicates that ZnO nanorods prepared by the catalyst-fee method are of high optical quality. Furthermore, time-resolved PL measurements at a free exciton peak were carried out at room temperature. The decay profiles were of double-exponential form, and the decay time constants of 180 ps and 1.0 ns were obtained using a least-square fit of the data. Excitation power-dependent PL of ZnO epilayers is also discussed.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.