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In this work, a planar electron emission device based on a graphene/hexagonal boron nitride (h-BN)/n-Si heterostructure is fabricated to realize highly monochromatic electron emission from a flat surface. The h-BN layer is used as an insulating layer to suppress electron inelastic scattering within the planar electron emission device. The energy spread of the emission device using the h-BN insulating layer is 0.28 eV based on the full-width at half-maximum (FWHM), which is comparable to a conventional tungsten field emitter. The characteristic spectral shape of the electron energy distributions reflected the electron distribution in the conduction band of the n-Si substrate. The results indicate that the inelastic scattering of electrons at the insulating layer is drastically suppressed by the h-BN layer. Furthermore, the maximum emission current density reached 2.4 A/cm2, which is comparable to that of a conventional thermal cathode. Thus, the graphene/h-BN heterostructure is a promising material for planar electron emission devices to obtain a highly monochromatic electron beam and a high electron emission current density.

We previously reported highly monochromatic electron emission from the planar-type electron emission devices based on a graphene/hexagonal boron nitride (h-BN) heterostructure. In this paper, the electron energy distribution (EED) of these devices is examined to clarify the mechanism of monochromatic electron emission. We find that the monochromaticity of the electron beam depends significantly on the electronic structure of the substrate material; for the devices with an n-type silicon substrate, the narrowest FWHM of the electron beam is 0.18 eV, whereas that of devices with a metallic (Nb) substrate is 0.33 eV. At the same time, simulations considering the electron scattering by phonons acceptably reproduced the shape of each EED spectrum considering the small energy loss due to out-of-plane acoustic phonon modes in h-BN. Thus, the monochromatic electron emission from the $\mathrm{graphene}/h$-$\mathrm{BN}/n$-$\mathrm{Si}$ device is ascribed to a combination of the narrow energy distribution of electrons at the conduction band of the n-$\mathrm{Si}$ substrate and small phonon energy of the h-BN insulating layer. These features also realize the excellent emission properties in addition to the monochromaticity of the beam, such as a high emission current density of $9.3{\mathrm{A}/\mathrm{cm}}^{2}$, insensitivity to environmental pressure up to 10 Pa, and long lifetime of more than 7 days with little decay.

Compact and radiation-tolerant radiation dosimeter without bias voltage application using solar cells such as CdTe was proposed for severe radiation environment near a nuclear reactor pressure vessel. In this work, γ-ray tolerance and γ-ray detection characteristics of CdTe solar cells were investigated. It was found that the CdTe solar cell has sufficient tolerance against γ-ray exposure up to 3 MGy. It was demonstrated that γ-ray induced current density linearly increased with increasing γ-ray intensity in the range up to approximately 1.5 kGy h−1. This result indicates that high dose-rate radiation detection can be performed using solar cells without voltage application. In addition, γ-ray sensitivity was successfully improved by a stack of CdTe solar cells with parallel connections. Furthermore, γ rays can be detected with high responsivity and small noise even under a high flux neutron environment.

The effect of gamma irradiation on two types (superstrate- and substrate-type) of CdS/CdTe photodiodes, which we have proposed as potential photoconducting films for compact image sensors with a field emitter array (FEA), was investigated. A 60Co gamma-ray source was employed, and the total gamma irradiation dose was more than 500 kGy. For the superstrate-type structure, the irradiation caused the short-circuit current density (JSC) to decrease, probably due to the resulting decreased transmittance of the glass substrate. On the other hand, little degradation of the I -V characteristics or spectral response was observed after the gamma irradiation for the substrate-type structure. These results suggest that, taking into account the decrease in transmittance of the glass substrate, the CdS/CdTe photodiodes have sufficient tolerance to high gamma-ray exposure. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We have already demonstrated that the graphitized mechanical pencil lead show superior field emission features in high emission current regime [1]. In this paper, we present the results of additional detailed analysis of field emission from completely graphitized pencil lead including Raman scattering, FIM/FEM images and energy distributions of emitted electrons as well as field emission characteristics also in low emission current regime. It is concluded again that the fully graphitized pencil lead is promising as low cost but superior field emitters

A prototype image sensor is developed using cadmium telluride-based photodiode and a volcano-structured FEA. Radiation tolerance of each component was tested by irradiating gamma-ray using cobalt-60 source. Gamma-ray tolerance of up to 1.2 MGy was confirmed for both FEA and photodiode.

The influences of gamma irradiation on CdS/CdTe photodiodes were investigated in order to evaluate their potential for applications to the radiation tolerant field emitter array (FEA) image sensor. It was found that the CdS/CdTe photodiodes have sufficient tolerance to high gamma-ray exposure more than 2 MGy. Furthermore, $I {-} V$ characteristics of CdS/CdTe photodiodes under gamma-ray irradiation were investigated. In the CdTe thickness of 6.5 $m\textbf{m}$, the change rate of current density increased with increase in the reverse bias voltage. On the other hand, in the case of 2.2 $m\textbf{m}$, the change rate of current density was almost constant irrespective of the reverse bias voltage. These results suggest that the increase in depletion layer width affects the change rate of current density.