Keio University · Materials Science
Professor Hideyuki Maki's research lab specializes in nanoscale optoelectronics and 2D materials, focusing on the development of advanced photonic and electronic devices using graphene, carbon nanotubes, and wide-bandgap semiconductors. Key research directions include on-chip silicon photonics with graphene-based emitters and optical switches, strain engineering of carbon nanotubes for tunable photoluminescence, and surface doping of ZnO for optoelectronic applications. The lab also explores redox-active molecular systems and novel electrical contact engineering for carbon nanotube devices to enhance device performance and stability.
Figures are computed from collected data and may differ slightly.
High-speed light emitters integrated on silicon chips can enable novel architectures for silicon-based optoelectronics, such as on-chip optical interconnects, and silicon photonics. However, conventional light sources based on compound semiconductors face major challenges for their integration with a silicon-based platform because of their difficulty of direct growth on a silicon substrate. Here we report ultra-high-speed (100-ps response time), highly integrated graphene-based on-silicon-chip b
We have fabricated a new device for applying uniaxial strain to an individual suspended SWNT, and the form and the photoluminescence (PL) of an individual suspended SWNT under stretching are investigated. The processes of deformation and break of a SWNT under stretching are directly observed by scanning electron microscopy (SEM). From the PL measurements, the emission energy shifts due to the band gap change are measured under the elastic strain. The behaviors of the emission shifts can be relat
Nitrogen radicals were irradiated on the (0001) and (0001) surfaces of the ZnO single crystals, and the stability and the states of N ions on the surfaces were investigated by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). On the (0001) surface, many N ions replaced the O ions of ZnO during annealing in oxygen gas or vacuum after nitrogen treatment. However, few N ions replaced the O ions of ZnO on the (0001) surface. These results suggest that the nitrogen doping
The electrochemically reversible photoluminescence of sulforhodamine B (SRB) anions is demonstrated based on the redox of Fe in a metallo-supramolecular polymer.
Graphene is a promising material for producing optical devices because of its optical, electronic, thermal, and mechanical properties. Here, we demonstrated on-chip optical switches equipped with a graphene heater, which exhibited high modulation speed and efficiency. We designed the optimal structure of the optical switch with an add/drop-type racetrack resonator and two output waveguides (the through and drop ports) by the electromagnetic field calculation. We fabricated the optical switch in
The new processes of current flow through electrodes at carbon nanotube (CNT)-electrode junctions were carried out to change the contact resistance of CNT conductors and the tunnel barriers of CNT quantum dots. When the current flow process was applied to CNT conductors with the Au/Ti electrodes deposited on multiwall CNTs (MWNTs), the contact resistance markedly decreased. This is caused by the formation of titanium carbide (TiC) at the electrode-nanotube junction due to the strong interaction
IR analyses such as Fourier transform infrared spectroscopy (FTIR) are widely used in many fields; however, the performance of FTIR is limited by the slow speed (∼10 Hz), large footprint (∼ millimeter), and glass bulb structure of IR light sources. Herein, we present IR spectroscopy and imaging based on multilayer-graphene microemitters, which have distinct features: a planar structure, bright intensity, a small footprint (sub-μm<sup>2</sup>), and high modulation speed of >50 kHz. We developed a
Microsized light sources with polarized or broadband emission can be used for a variety of applications. However, the system directly generating polarized and broad-spectrum light without using polarizers has not been established. Here, we found that a nano-device of densely packed and highly aligned carbon nanotube (CNT) films on silicon chips can emit polarized light with a broad spectrum. We observed spatial emission patterns that are dependent on the angle between the electrical bias and the
We have fabrficated field-effect transistors with single-walled carbon nanotube films using various work-function metals (Mg, Al, Ti, and Ni) as the source and drain electrodes to control the transfer characteristic. The n-type transfer characteristic is obtained from the device with low-work-function metal (Mg), and the p-type characteristic is obtained from the device with medium- and high-work-function metals (Al, Ti, and Ni). The ambipolar characteristic of the device with Mg electrodes in a
Graphene is a promising material for developing high-speed and wide-wavelength-range photodetectors. However, since the polarities of the photovoltages at each graphene/electrode interface of two electrodes on both ends of the graphene are opposite, they are canceled out under macroscopic light irradiation to the photodetectors. In this study, we propose two graphene-based photodetectors with different asymmetric device structures that can suppress the cancelation of photovoltage at the interfac
A single-photon source (SPS) based on a single-walled carbon nanotube (SWCNT) is a promising candidate for uncooled on-chip quantum information optoelectronics because a single photon can be generated at both room temperature and telecommunication wavelengths on silicon chips. However, for the applications of quantum information, such as quantum computing and quantum cryptography, higher performance SPSs that exhibit both high purity and high efficiency of single-photon generation are required.
A ZnO crystal of wurtzite-type structure has polar surfaces of (0001) and (0001), which are terminated by Zn and O ions, respectively. Observation conducted by atomic force microscopy showed that step/terrace structures were formed on the (0001) and (0001) surfaces, whose step height was predominantly half of lattice parameter, c 0 . The ionic arrangement of the surfaces was determined by coaxial impact-collision ion scattering spectroscopy (CAICISS); the CAICISS spectra had a periodicity of 60°
We report the development of narrow-linewidth photoluminescence (PL) devices based on single-walled carbon nanotubes (SWNTs) and silicon photonics with microresonators and waveguides that can generate in-line PL at a telecommunication wavelength of 1.55 μm band. We coupled the PL from SWNTs to the ring and disk resonators to obtain low-background narrow-linewidth PL. From the ring resonator device, narrow-linewidth PL emission with a high Q factor of ∼3000 is obtained. In addition, the PL emissi
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