Yoichiro Neo's research while affiliated with Shizuoka University and other places

Publications (167)

Article
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Carbon nanotubes (CNTs) are ultimately small structures, attractive for future nanoelectronics. CNT-bundles on Si nanostructures can offer an alternative pathway to build hybrid CMOS-compatible devices. To develop a simple method of using such CNT-bundles as transistor channels, we fabricated semiconductor single-walled CNT field-effect transistors...
Article
A TiO2/Si hybrid photoelectrode (HPE) (photoanode) consisting of TiO2 and a Si n++p++nn++ photoelectrode, and a Pt-free counter photoelectrode (photocathode) consisting of Au or Ag clusters and a Si n++pp++ junction were manufactured and investigated. TiO2 was deposited on the Si n++p++nn++ photoelectrode to widen the spectral selectivity from UV t...
Article
Electron transport through a few-donor cluster flanked by acceptors is studied by first-principles and semi-empirical simulations in gated Si-nanowire transistors with n ⁺ electrostatically-doped source/drain. Local density-of-states spectra are probed by electrical characteristics at room temperature for clarifying modifications induced by accepto...
Article
The conduction band discontinuity between n-type Si substrates and anatase TiO 2 films has been investigated. n-type Si substrates with three different dopant concentrations were used as a substrate for TiO 2 thin-films: N D = 10 15–16 cm ⁻³ (as n-Si); N D = 10 17–18 cm ⁻³ (as n ⁺ -Si); N D = 10 20–21 cm ⁻³ (as n ⁺⁺ -Si). The translation of X-ray p...
Article
This paper proposes a new operation method for an image pickup tube under high-temperature conditions. The landing energy of an electron beam is set at a value for the secondary electron yield above 1.0. The mesh electrode, which is located in front of the image plate, can act as a potential barrier and control the surface potential of the image pl...
Article
In this study, highly-aligned and molecularly oriented poly(vinylidene fluoride/trifluoroethylene) [P(VDF/TrFE)] nanofiber webs were fabricated and their piezoelectric response was investigated. Using systematic post-treatments under appropriate conditions, a significant enhancement of the piezoelectric response in the P(VDF/TrFE) nanofiber webs wa...
Article
Highly efficient electron emission of 48.5% was demonstrated by a graphene/oxide/semiconductor (GOS) structure. The main factors contributing to this performance were investigated by analyzing the energy distributions of the emitted electrons and the current conduction mechanism through the oxide layer. The energy level of the lower tail of the ele...
Article
Full-text available
An oscillating piezoresistive microcantilever (MC) coated with an aluminum (Al)-doped zinc oxide (ZnO) nanorods was used to detect carbon monoxide (CO) in air at room temperature. Al-doped ZnO nanorods were grown on the MC surface using the hydrothermal method, and a response to CO gas was observed by measuring a resonant frequency shift of vibrate...
Article
A field emission image sensor (FEIS) that consists of a field emitter array (FEA) and a cadmium telluride-based diode was proposed for use in the nuclear decommissioning of the Fukushima Daiichi nuclear power plant. FEAs and cadmium telluride/cadmium sulfide diode were irradiated with $\gamma $ -rays for a dozen times, each with a dose of irradia...
Article
We experimentally demonstrated a giant Goos-Hänchen (GH) shift in a metal-dielectric multilayer Fano structure. The observed GH shift was 0.176 mm, which corresponded to (GH shift/λ) = 493, where λ is the incident wavelength. A unique feature of this giant GH shift was that it occurred without attenuation, i.e., reflectivity ∼1, due to Fano interfe...
Article
A graphene-oxide-semiconductor (GOS) planar-type electron source was fabricated by direct synthesis of graphene on an oxide layer via low-pressure chemical vapor deposition. It achieved a maximum electron emission efficiency of 32.1% by suppressing the electron inelastic scattering within the topmost gate electrode using a graphene electrode. In ad...
Article
Full-text available
A microcantilever (MC) coated by Al-doped ZnO nanorods (AZNRs) was used for carbon monoxide (CO) detection at ambient temperature. Very high sensitivity (on the order of femtograms) was obtained, which is caused by the intense adsorption of CO molecules on the AZNR surface. After the samples had been prepared and characterized, the effects of the p...
Article
In this study, electron emission model is investigated for heavily phosphorus‐doped n‐type diamond having positive electron affinity surface. Ultraviolet photoelectron spectroscopy (UPS) is conducted to determine the band structure of the diamond. In addition, combined UPS and field‐emitted electron spectroscopy is carried out in order to determine...
Article
Zinc oxide (ZnO) nano-rods has widely been investigated as a promising material for photo-catalysis, due to its high photocatalytic activity for the ambient gas molecules. Well-aligned ZnO nano-rods arrays were obtained by the two steps growth. Firstly, seeding layer deposition by RF magnetron sputtering, and secondly, nano-rods growth by hydrother...
Article
In this work, effects of annealing temperature of seeding layer on structural properties and morphologies of Ga/F co-doped ZnO nanostructures synthesized by hydrothermal process were investigated by varying the annealing temperature of seed layer as 300-500 °C. The ZnO seeding layers were deposited onto cleaned glass substrates by dip-coating techn...
Article
We observed positive and negative Goos–Hänchen (GH) shifts in plasmon-induced transparency (PIT) in a metal–insulator–metal (MIM) multi-layer structure based on the attenuated total reflection response. Here, the MIM waveguide (WG) mode and the surface plasmon polariton (SPP) resonance act as low- and high-Q resonances, respectively. SPP also induc...
Article
Full-text available
We demonstrated tailored plasmon-induced transparency (PIT) in a metal (Au)-insulator (SiO2)-metal (Ag) (MIM) structure, where the Fano interference between the MIM waveguide mode and the surface plasmon polariton (SPP) resonance mode induced a transparency window in an otherwise opaque wavenumber (k) region. A series of structures with different t...
Article
In this study, photoconductor made of amorphous selenium (a-Se) is studied to improve a sensitivity of vacuum-tube type photodetectors. An electrochemical process was applied to a-Se films to form a p-n structure within the film. The formation of p-n structure was confirmed by time-of-flight secondary ion mass spectroscopy as well as its electronic...
Article
Full-text available
Resonance frequency shift of a zinc oxide- (ZnO-) functionalized microcantilever as a response to carbon monoxide (CO) gas has been investigated. Here, ZnO microrods were grown on the microcantilever surface by a hydrothermal method. The measurement of resonance frequency of the microcantilever vibrations due to the gas was carried out in two condi...
Article
Full-text available
For future broadband wireless links, we have designed a 300 GHz band traveling wave tube (TWT) with a folded waveguide fabricated by microelectromechanical systems (MEMS). The TWT operates at a beam voltage of 12 kV and a beam current of 8.3 mA. The classical large signal simulation code predicts the output power greater than 1 W and gain larger th...
Article
We experimentally demonstrated a plasmon-induced transparency in a metal-insulator-metal (MIM) structure based on the attenuated total reflection (ATR) response. Here, the MIM waveguide (MIMWG) mode and the surface plasmon polariton (SPP) resonance mode acted as low- and high-Q resonance modes, respectively. The dependence of the resonance angles o...
Article
Photonic structures created by coupling a narrow resonance to a broad resonance can significantly improve the sensitivity of optical sensors. We investigated a planar metalinsulator- metal (MIM) multilayered structure using attenuated total reflection to couple surface plasmon polaritons with the waveguide (WG) mode. A plasmon-induced transparency...
Conference Paper
A growing demand on incident detection is recognized since the Great East Japan Earthquake and successive accidents in Fukushima nuclear power plant in 2011. Radiation tolerant image sensors are powerful tools to collect crucial information at initial stages of such incidents. However, semiconductor based image sensors such as CMOS and CCD have lim...
Article
We report optically modulated electron emission from gated p-type silicon field emitter arrays (Si-FEAs). The device's “volcano” structure is designed to control the photoexcitation of electrons by transmitting light through the small gate aperture, thereby minimizing the photogeneration of slow diffusion carriers outside the depletion region in th...
Article
The authors have developed a highly sensitive, compact image sensor comprising a field emitter array (FEA) and a high-gain avalanche rushing amorphous photoconductor (HARP) target with the ultimate aim of developing an ultrahigh sensitivity, compact, high-definition television camera. Double-gated field emitters have the advantage of a compact elec...
Article
In this article, a field-induced electron emission from hydrogen (H)-terminated surface of heavily phosphorus (P)-doped diamond is discussed based on the barrier lowering model. Ultraviolet photoelectron spectroscopy suggested that an upward band bending of 1.45 eV existed at the surface of the diamond. A field emission characteristic as a function...
Article
We have developed a highly sensitive, compact image sensor that comprises a field emitter array (FEA) and a high-gain avalanche-rushing amorphous photoconductor target, with the ultimate aim of developing an ultrahighly sensitive, compact, high-definition television camera. Double-gated FEs have an advantage of having a compact electron beam focusi...
Article
Double-gated Spindt-type field emitter arrays with volcano structures were fabricated using a double-layered photoresist as a lift-off layer for image sensor application. The gate aperture height and emitter tip angle were varied to optimize the device structure, wherein the gate aperture height was changed by controlling the etch-back time during...
Article
Photo-assisted electron emission from a p-type silicon field emitter array (FEA) excited by laser pulses with 405 nm wavelength is investigated for generating electron bunches at high frequency. By using a volcano structure, the photoresponse of the current pulses is less than 2 ns, which is limited by the response time of a used current amplifier....
Article
The electron source generating density modulated electron beam (a train of electron beam pulses) at high frequency directly from the cathode surface has attracted significant interest since they could be used in a wide variety of vacuum electronics devices, such as compact microwave sources [1-4], ultrafast electron microscopy [5], or electron beam...
Article
We have fabricated P(VDF-TrFE) nanofiber webs by electrospinning. Highly aligned nanofiber webs with high uniformity and a smooth surface were fabricated. To obtain single-crystalline P(VDF-TrFE) nanofibers, we have studied the effect of stretching and annealing on the P(VDF-TrFE) nanofiber web. Three samples were fabricated: as-electrospun, anneal...
Article
Full-text available
We have developed a multi-gated field emitter (FE) such as a quadruple-gated FE with a three-stacked electrode lens and a quintuple-gated FE with a four-stacked electrode lens. Both the FEs can focus the electron beam. However, the quintuple-gated FE has a stronger electron convergence than the quadruple-gated FE, and a beam crossover is clearly ob...
Article
To improve QE of the photocathode using surface plasmon resonance, we have employed the new arrangement of the photocathode and incident light, where the direction of the surface plasmon coincides with the momentum direction of the emitting electrons. We have achieved the QE by 103 times larger than that of the conventional photocathode using surfa...
Conference Paper
We have fabricated two type of graphite field emission cathodes: graphite nanospines (GNS) and graphite field emitters inflamed at high temperatures (GFEIHT) and applied for X-ray tubes using these cathodes. The morphologies and structures of the two cathodes were quite different. However, these emitters have excellent field emission characteristic...
Conference Paper
Graphene/hexagonal boron nitride (h-BN) was characterized. Field emission from graphene/h-BN/Si structure showed low threshold voltage and enhanced emission current. Fowler-Nordheim (F-N) plots were applied to discuss the obtained field emission properties. We also examined work function using ultraviolet photoelectron spectroscopy (UPS). The obtai...
Conference Paper
We have studied the photoassisted electron emission from a p-type silicon field emitter array under illumination of laser lights with 633 nm and 405 nm wavelengths. The increase of the emission current under light illumination is proportional to the emission current in the dark. The significant influence of the polarization in photoassisted emissio...
Conference Paper
In this study, an attempt was made to reduce dark current of amorphous-selenium (a-Se) based photodetector. An electro-chemical method was utilized to incorporate chlorine (Cl) into a-Se, in order to form a blocking junction within a-Se film. Current versus applied voltage characteristic of Cl-incorporated film showed a rectifying characteristic, w...
Conference Paper
The photoresponse of electron emission from metal-oxide-semiconductor (MOS) cathodes based on nanocrystalline silicon is experimentally studied for optically generating a train of short electron bunches. Nanocrystalline silicon film was prepared by pulsed laser ablation using an Nd:YAG laser with the fourth harmonic (266 nm). We obtained a pulsed e...
Article
We present the electron optical properties of a newly designed microcolumn. The microcolumn consists of an objective lens and an electron gun, which is composed of a microscale field emitter and a condenser lens. An acceleration lens was used as the objective lens. Each component was optimized to maximize its own function while minimizing its impac...
Article
We investigate the mechanism by which small organic molecules adsorbed on a field emission tip form cloverleaf patterns. This phenomenon was discovered by Müller in 1950. Many theories have been subsequently proposed for the formation of these patterns. However, their formation mechanism is not well understood. In a previous study, we obtained imag...
Article
We investigate the mechanism by which small organic molecules adsorbed on a field emission tip form cloverleaf patterns. This phenomenon was discovered by Müller in 1950. Many theories have been subsequently proposed for the formation of these patterns. However, their formation mechanism is not well understood. In a previous study, we obtained imag...
Conference Paper
To investigate temporal change of the output signal from the CdTe detectors, optical laser pulses was used for carrier generation. Electrical responses from the CdTe detectors were detected as a function of generated carrier density and applied bias voltage. Temporal change of the internal electric field at defined position in the CdTe detector can...
Conference Paper
This report describes about the fundamental experimental results for x-ray imaging device which consists of a Schottky Cadmium Telluride (CdTe) diode and a scanning focused electron beam. It successfully demonstrated that the two kinds ways for reading out signal by electron beam. It was investigated in details about the output current dependencies...
Conference Paper
The novel photocathode consists of a quartz right triangle prism and aluminum thin film, that was optimized for perfect photon adsorption. The emission current properties as function of incident angle showed the local maximum in agreement with the condition for maximum field enhancement. Furthermore it was demonstrated by evaluating energy spectrum...
Conference Paper
The enhancement of electron emission by laser illumination of a metal-oxide-semiconductor (MOS) cathode based on nanocrystalline silicon was investigated. An increase of the emission current under blue laser irradiation was proportional to the incident laser power. The influence of light modulation on the emission current was also investigated. We...
Article
Characteristics of CdTe radiation detectors are studied using laser pulses. To improve the spatial and time resolution of carrier generated position and time, optical laser pulses were used for carrier generation and the electrical response from the CdTe radiation detectors were detected as a function of irradiated position and time. The detector m...
Article
Pulse laser was due to investigate characteristics of Schottky-diode type CdTe detector. The pulse laser was irritated to cleaved surface of the CdTe detector to control incident position and time accurately. Even though one-photon energy of the plse laser is different from that of γ-ray mainly detected by the CdTe detectors, amount of pulse energy...
Chapter
Full-text available
Summary form only given. Commercial expandable graphite was heat at 900 °C to get the worm-like graphene nanosheets. Using sulfuric acid and potassium permanganate to oxidize the expanded graphene nanosheet could further minish the thickness of graphene oxide sheet to less than 1nm, and this way to get the graphene was proved to be mass producible...
Article
A crossover point was observed with a fabricated quintuple-gated micro-column by an enhanced knife-edge measurement. Developing this result, we designed a new tiny electron beam microscope using multi-gated micro-column by using scale down rule of a micro-column. A beam spot size of the proposed device was estimated to be 50nm by an electron beam t...
Article
Full-text available
A field emitter array (FEA) with a five-stacked gate electrode, that is, a quintuple-gated FEA with a four-stacked electrode lens, was fabricated. The four-stacked electrode forms an einzel lens, where the second and third electrodes are connected through a contact hole. Because the electron velocity of the einzel lens in a quintuple-gated FEA is s...
Article
Abstract - We have designed and fabricated a novel triple-gated electron beam gun capable of generating a parallel electron beam. The beam profile was measured by the slit weeping method and we have confirmed the formation of parallel beam.
Article
A novel photocathode using surface plasmon resonance has been proposed. We designed a photocathode and measured the photoelectron current by changing the light incident angle. We observed the enhancement of the photoelectron current in the region predicted theoretically. The photoelectron current linearly increases with increase of the incident las...
Article
Optically pulsed modulation of a nanocrystalline silicon based silicon metal-oxide-semiconductor cathode fabricated on p-type silicon has been studied using a He-Ne laser mechanically chopped When shining a MOS cathode, the emission current was quickly responded to on-off of the laser. In addition, the energy distributions of emitted electrons were...
Article
Thermoacoustic carbon nanotube (CNT) speakers were fabricated using CNT webs spun from a multiwalled carbon nanotube (MWNT) array of 0.8–1.6 mm height. The generated sound pressure level (SPL) showed a linear relationship with frequency over a wide range from 10 Hz to 40 kHz with a slope of 6 dB/octave. In addition to this, significantly broad and...
Article
Full-text available
Thermoacoustic carbon nanotube (CNT) speakers were fabricated using CNT webs spun from a multiwalled carbon nanotube (MWNT) array of 0.8--1.6 mm height. The generated sound pressure level (SPL) showed a linear relationship with frequency over a wide range from 10 Hz to 40 kHz with a slope of 6 dB/octave. In addition to this, significantly broad and...
Article
<110>-oriented single crystal magnetite (Fe3O4) whiskers 30 to 300 nm in diameter were synthesized on a stainless steel plate by means of the combustion flame thermal oxidation process. An electron source with this single magnetite whisker was fabricated by using a micro-sampling instrument in an FIB system. The temperature dependence of the spin p...
Article
The carrier transportation properties of a P-intrinsic-N (PiN) type CdTe diode detector for radiation spectrography was evaluated under the non-polarized and polarized condition with high speed signal processing method for a practical photon-counting system. The rise-up time distribution in each energy region was obtained by our system in each oper...
Article
The traditional X-ray CT measurement takes long time to construct scanning image, because X-ray sources and detectors are revolved around objects to get over 180 projection data for reconstructing an inner structures image of objects. For this reason, X-ray CT scan system has been hardly used in high throughput fields. In this paper, we proposed ne...
Conference Paper
We have proposed the new micro column electron beam microscope fabricated with multi-gated field emitter array based on the first result that a crossover successfully observed with quintuple-gated FEA. In order to realize the fine focused electron beam less than several ten nm in diameter, the initial emission angle after emitting from tip surface...
Article
Cadmium telluride (CdTe) detector has been used to detect thermal neutrons; along with gadolinium (Gd) used as a neutron converter. Simulation results show that the appropriate thickness of Gd film for CdTe detector is 25 mum. The Gd/CdTe detector shows the 80 keV, 89 keV and 182 keV gamma ray emission peaks from 155Gd(n, gamma)156Gd and 157Gd(n, g...
Article
To identify the factor impairing the material identification parameters, which is provided by the dual-energy X-ray computed tomography method using a conventional X-ray tube and a CdTe detector, linear attenuation coefficient was measured by the radioactivity of radio isotopes and compared with theoretical figure. In our study, the atomic number a...
Article
Pulsed thermionic emission from multiwalled carbon nanotube fibers has been demonstrated. From fibers with diameter of 150 μm we obtained an emission current of 16 μA at a repetition rate of 1 kHz. A comparison between our CNT fibers and a tungsten filament is also presented.