[en] This paper presents two passive thermoluminescence radon accumulating detectors. These detectors are suitable for monitoring air radon concentration indoors, outdoors and in wells of mines. The detectors have advantages of small size, light wight and convenient to handle. Measurement results are proved to be reliable through the comparison of passive accumulating detectors and in-site use of them

[en] In this paper, the influence of different environmental conditions, substrates, micromachining processes, areas and patternings on the performances of PECVD SiO₂/Si₃N₄ double-layer electrets were studied for its application in micro-devices. Various samples were prepared and then charged by the negatively corona charging method. The charge decays at either 250°C or 95%RH were observed to reveal the chargeability and charge stability. Finally, a micro power generator with patterned PECVD SiO₂/Si₃N₄ double-layer electret was presented briefly as demonstration. The results show that all these conditions that conventionally or even unavoidably happen in the fabrication process of electret micro-devices had more or less impact on the electret performance. It is crucial that the electret should be as large area as possible and kept from the micromachining processes and humid condition to the best. Our micro power generator with 2mm rectangular array of PECVD SiO₂/Si₃N₄ double-layer electret had the 5μW output power at 20Hz and 0.7g. (paper)

[en] A large-volume microwave plasma with good stability, uniformity and high density is directly generated and sustained. A microwave cavity is assembled by upper and lower metal plates and two adjacently parallel rectangular waveguides with axial slots regularly positioned on their inner wide side. Microwave energy is coupled into the plasma chamber shaped by quartz glass to enclose the space of working gas at low pressures. The geometrical properties of the source and the existing modes of the electric field are determined and optimized by a numerical simulation without a plasma. The calculated field patterns are in agreement with the observed experimental results. Argon, helium, nitrogen and air are used to produce a plasma for pressures ranging from 1000 to 2000 Pa and microwave powers above 800 W. The electron density is measured with a Mach-Zehnder interferometer to be on the order of 10¹⁴ cm^-3 and the electron temperature is obtained using atomic emission spectrometry to be in the range 2222-2264 K at a pressure of 2000 Pa at different microwave powers. It can be seen from the interferograms at different microwave powers that the distribution of the plasma electron density is stable and uniform.

[en] GaAs-Alsub(x)Gasub(1-x)As heterojunction was grown by liquid phase epitaxy at low growth temperature 650-700 deg. C. The series resistance of heterojunction with DH laser structure was measured. Doping properties of Mg in GaAs and Alsub(x)Gasub(1-x)As were investigated. It is found that impurity concentration of Mg as high as 10¹⁸cm^-3 can be doped easily. The Shubnikov-de-Haas oscillation was observed in GaAs-N Alsub(0.35)Gasub(0.65)As heterointerface. It is demonstrated that in these heterointerfaces there exists 2DEG with some contribution from 3D electron of N-AlGaAs layer. (author)

[en] Highlights: • The optimization design and simulation of a betavoltaic battery were studied. • The optimal thickness of the titanium tritide film was obtained. • The enery deposition distribution of the β particles in the silicon PN junction was obtained. • The output performance of the betavoltaic battery was optimized. - Abstract: This article presents the optimization design and simulation of a betavoltaic battery composed of a silicon p-n junction converter and a titanium tritide film as an isotope source. The self-absorption of β particles emitted from the tritium radioisotope in the titanium tritide film and the energy deposition of β particles in the silicon converter are investigated by the Monte Carlo simulation with the Geant4 radiation transport toolkit. The relationships between doping concentrations and basic parameters such as depletion region width, minority carrier diffusion length and leakage current of the PN junction are discussed through the calculation formulas. By optimizing the doping concentrations in the P-type and N-type regions, the optimized betavoltaic battery can maximize the output power and the conversion efficiency based on the energy deposition in the silicon. The results show that the optimal thickness of the titanium tritide film is about 0.7 µm and the optimal doping concentrations of the battery with a PN junction depth of 50 nm are $N_a=5.75\times {10}^{19}\mathrm{c}{\mathrm{m}}^{-3}$,$N_d=2.95\times {10}^{18}\mathrm{c}{\mathrm{m}}^{-3}$. Under these parameters, the size $1\mathrm{m}\mathrm{m}\times 1\mathrm{m}\mathrm{m}$ proposed battery with 2.9 mCi/mm^{2 3}H can achieve the output power 0.902 nW and the conversion efficiency 0.91%. The open circuit voltage, short circuit current and fill factor of the battery are 0.389 V, 3.03 nA and 0.766, respectively.

[en] The electron density in a microwave plasma torch at atmospheric pressure was measured with a Mach-Zehnder interferometer. The electron density is on the order of 10¹⁷/cm³, one order higher than that deduced from the Stark broadening of spectral lines, and increases with the increase in the microwave power. The spatial distribution of the electron density was obtained. The highest electron density locates at the symmetrical axis of the plasma torch and decreases radially. It was found that the electron density fluctuates within a range of 0.3 with the time under the same experimental conditions.

[en] We present the combined field integral equation (CFIE) method for analysing radio-frequency coil arrays in high-field magnetic resonance imaging (MRI). Three-dimensional models of coils and the human body were used to take into account the electromagnetic coupling. In the method of moments formulation, we applied triangular patches and the Rao-Wilton-Glisson basis functions to model arbitrarily shaped geometries. We first examined a rectangular loop coil to verify the CFIE method and also demonstrate its efficiency and accuracy. We then studied several eight-channel receive-only head coil arrays for 7.0 T SENSE functional MRI. Numerical results show that the signal dropout and the average SNR are two major concerns in SENSE coil array design. A good design should be a balance of these two factors

[en] A comparative study of selective dry and wet etching methods for germanium–tin (Ge_1−xSn_x) alloys (3.5% < x < 7.7%) and germanium (Ge) is carried out. Both etching methods are optimized from the perspectives of selectivity and morphology, and then compared. A special behavior of the selective dry etching process is discovered and explained, whereby the selectivity has a dramatic increase to as high as 336 when the Sn concentration is above 6%. Different morphologies of suspended microstructures fabricated by different etching methods are investigated. Comparative study shows that the selective dry etching is a better choice for high Sn concentration GeSn (above 7%) against Ge to have better morphology, selectivity and verticality. While for low Sn concentration GeSn (below 6%), wet etching is a better way to fabricate a suspended GeSn microstructure on Ge. This work provides a comparative understanding of both methods of selective etching for GeSn. This comparative understanding is expected to be applied in the processing of next generation electronic and photonic devices. (paper)

[en] Highly strained InGaAs:Bi quantum wells (QWs) were grown on (001)-oriented GaAs substrates by molecular beam epitaxy (MBE). Photoluminescence (PL) reveals strong improvements in the optical properties evidenced by 10 times enhancement in PL intensity and extended emission wavelength up to 1.29 μm when Bi is introduced to InGaAs/GaAs QWs. The improved optical quality results from the Bi surfactant effect as well as the Bi incorporation. Post growth thermal annealing shows that Bi atoms in InGaAs/GaAs QWs do not show good thermal stability at 650 °C and tend to diffuse out of the QWs resulting in large wavelength blue-shifts.

[en] Intermediate band solar cells have attracted significant interest as a possible means of achieving high conversion efficiency. Under optimized growth parameters, we successfully achieve a high density of uniform InAs QDs grown on various matrixes by molecular beam epitaxy. Incorporating N atoms into GaAs and AlGaAs barriers effectively compensates the internal compressive strain and avoids formation of dislocations and defects. The 50 stacking of high density and uniform InAs QDs was demonstrated without detectable dislocations using 26 nm GaNAs as a barrier. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)