The influence of oxygen content on photoluminescence from Er-doped SiOx

SiOx films with oxygen concentrations ranging 13-46 at.% were deposited by plasma enhanced chemical vapor deposition (PECVD) technique using: pure SiH4 and N2O mixture. Erbium was then implanted at an energy of 500 KeV with dose of 2x10(15) ions/cm(2). The samples were subsequently annealed in N-2 for 20 sec at temperatures of (300-950 degrees C). Room temperature (RT) photo-luminescence (PL) data were collected by Fourier Transform Infrared Spectroscopy (FTIS) with an argon laser at a wavelength of 514.5 nm and an output power from 5 to 2500 mw. The intense room-temperature luminescence was observed around 1.54 mu m. The luminescence intensity increases by 2 orders of magnitude as compared with that of Er-doped Czochralski (CZ) Si. We found that the Er3+ luminescence depends strongly on the SiOx microstructure. Our experiment also showed that the silicon grain radius decreased with increasing oxygen content and finally formed micro-crystalline silicon or nano-crystalline silicon. As a result, these silicon small particles could facilitate the energy transfer to Er3+ and thus enhanced the photoluminescence intensity.

Photoluminescence measurements on erbium-doped silicon

Erbium-implanted silicones were treated by lamp-heating rapid thermal annealing (RTA). Two types of erbium-related photoluminescence spectra appear under different anneal temperatures. 750 degrees C annealing optimizes the luminescence intensity, which does not change with anneal time. Exciton-mediated energy transfer model in erbium-doped silicon was presented. The emission intensity is related to optical active erbium concentration, lifetime of excited Er3+ ion and spontaneous emission time. The thermal quenching of the erbium luminescence in Si is caused by thermal ionization of erbium-bound exciton complex and nonradiative energy backtransfer processes, which correspond to the activation energy of 6.6 meV and 47.4 meV respectively.

Effect of volume ratio on thermocapillary flow in liquid bridges of high-Prandtl-number fluids

In present study, the transition of thermocapillary convection from the axisymmetric stationary flow to oscillatory flow in liquid bridges of 5cst silicon oil (aspect ratio 1.0 and 1.6) is investigated in microgravity conditions by the linear instability analysis. The corresponding marginal instability boundary is closely related to the gas/liquid configuration of the liquid bridge noted as volume ratio. With the increasing volume ratio, the marginal instability boundary consists of the increasing branch and the decreasing branch. A gap region exists between the branches where the critical Marangoni number of the corresponding axisymmetric stationary flow increases drastically. Particularly, a unique axisymmetric oscillatory flow (the critical azimuthal wave number is m=0) in the gap region is reported for the liquid bridge of aspect ratio 1.6. Moreover, the energy transfer between the basic state and the disturbance fields of the thermocapillary convection is analyzed at the corresponding critical Marangoni number, which reveals different major sources of the energy transfer for the development of the disturbances in regimes of the increasing branch, the gap region and the decreasing branch, respectively.

Instabilities in a non-transferred direct current plasma torch operated at reduced pressure

Using an oscilloscope, a high-speed video camera and a double-electrostatic probe system, the periodicity and amplitude of the fluctuations in arc voltage, jet luminance and ion saturation current of a plasma jet were monitored to investigate various sources of instabilities and their effects in a non-transferred dc plasma torch operated at reduced pressure. The results show that besides a 300 Hz main fluctuation inherited from the power supply, arc voltage fluctuation of 3–4 kHz with an amplitude less than 5% of the mean voltage was mainly affected by the total gas flow rate. The arc voltage fluctuation can affect the energy distribution of the plasma jet which is detectable by electrostatic probes and a high-speed video camera. The steadiness of energy transfer is also affected by the laminar or turbulent flow state of the plasma.

Plasma and electrode emissions from a 1 kW hydrogen-nitrogen arcjet thruster

Arc root behavior affects the energy transfer and nozzle erosion in an arcjet thruster. To investigate the development of arc root attachment in 1 kW class N2 and H2-N2 arcjet thrusters from the time of ignition to the stably working condition, a kinetic series of end-on view images of the nozzle obtained by a high-speed video camera was analyzed. The addition of hydrogen leads to higher arc voltage levels and the determining factor for the mode of arc root attachment was found to be the nozzle temperature. At lower nozzle temperatures, constricted type attachment with unstable motions of the arc root was observed, while a fully diffused and stable arc root was observed at elevated nozzle temperatures.

离子束辐照结合组织培养在植物诱变中的研究进展

简述了植物组织培养方法与离子束辐射相结合这一新诱变技术的研究进展,从原理、操作步骤、分子机理等诸方面对该方法进行了阐释。该诱变技术具备传统辐射诱变技术所不具备的优势,从而能够为利用无性繁殖技术进行后代繁衍的植物提供新的育种思路。与此同时,使用该方法还能够开展植物组织细胞的传能线密度(Linear energy transfer,LET)生物学效应的研究,从理论上及实践上进一步优化该技术。

重离子照射肿瘤细胞的相对生物学效应值

对人肝癌细胞SMMC–7721细胞和黑色素瘤细胞A375细胞,进行80.55MeV12C6+离子、X射线和γ射线照射,通过克隆存活实验获剂量–存活曲线,以X射线或γ射线为标准,计算重离子的相对生物学效应(Relative biological effectiveness,RBE)。结果显示,两种细胞的重离子RBE值都大于1,且分次照射的RBE大于单次照射。重离子照射SMMC–7721细胞的RBE高于A375细胞,分次照射的差异更明显。重离子具有独特的物理特性及高传能线密度(Line energy transfer,LET)下的强杀伤作用,可有效杀伤不同肿瘤细胞,减弱了细胞间的敏感性差异。临床的分次照射重离子治疗时,细胞的亚致死修复明显降低,可采取较少的照射次数达到杀伤肿瘤的目的,提高肿瘤治疗效率,减轻病人痛苦。

Behavior of crystalline silicon under huge electronic excitations: A transient thermal spike description

Recent experimental works devoted to the phenomena of mixing observed at metallic multilayers Ni/Si irradiated by swift heavy ions irradiations make it necessary to revisit the insensibility of crystalline Si under huge electronic excitations. Knowing that Ni is an insensitive material, such observed mixing would exist only if Si is a sensitive material. In order to extend the study of swift heavy ion effects to semiconductor materials, the experimental results obtained in bulk silicon have been analyzed within the framework of the inelastic thermal spike model. Provided the quenching of a boiling ( or vapor) phase is taken as the criterion of amorphization, the calculations with an electron-phonon coupling constant g(300 K) = 1.8 x 10(12) W/cm(3)/K and an electronic diffusivity D-e(300 K) = 80 cm(2)/s nicely reproduce the size of observed amorphous tracks as well as the electronic energy loss threshold value for their creation, assuming that they result from the quenching of the appearance of a boiling phase along the ion path. Using these parameters for Si in the case of a Ni/Si multilayer, the mixing observed experimentally can be well simulated by the inelastic thermal spike model extended to multilayers, assuming that this occurs in the molten phase created at the Ni interface by energy transfer from Si. (C) 2009 Elsevier B. V. All rights reserved.

Experimental study on heavy ion single event effects in SOI SRAMs

Silicon-on-insulator (SOI) technologies have been developed for radiation-hardened military and space applications. The use of SOI has been motivated by the full dielectric isolation of individual transistors, which prevents latch-up. The sensitive region for charge collection in SOI technologies is much smaller than for bulk-silicon devices potentially making SOI devices much harder to single event upset (SEU). In this study, 64 kB SOI SRAMs were exposed to different heavy ions, such as Cu, Br, I, Kr. Experimental results show that the heavy ion SEU threshold linear energy transfer (LET) in the 64 kB SOI SRAMs is about 71.8 MeV cm(2)/mg. Accorded to the experimental results, the single event upset rate (SEUR) in space orbits were calculated and they are at the order of 10(-13) upset/(day bit).

Survivin expressions in human hepatoma HepG2 cells exposed to ionizing radiation of different LET

Survivin is a member of the inhibitors of apoptosis (IAP) protein family that interferes with post-mitochondrial events including activation of caspases. To examine the regulation of survivin expression in response to irradiation with different linear energy transfer (LET), human hepatoma HepG2 cells were irradiated in vitro with X-rays and carbon ions. Cellular sensitivities to low- and high-LET radiation were determined by colony formation. Survivin expression at mRNA and protein level were measured with RT-PCR and Western blot analyses, respectively. Radiation-induced cell cycle arrest and apoptosis were investigated with flow cytometry. We found that low-LET X-rays induced dose-dependent increases in survivin expression. After exposure to high-LET carbon ions, survivin expression gradually increased from 0 to 4 Gy, and then declined at 6 Gy. More pronounced survivin expression, stronger G(2)/M phase arrest was observed after exposure to carbon ions in comparison with X-rays at doses from 0 to 4 Gy. These observations indicate that there is a differential survivin expression in response to different LET radiations and the cycle arrest mechanism may be associated with it. In addition, our data on induction of apoptosis are compatible with the assumption that survivin expression induced by low-LET X-rays radiation may play a critical role in inhibiting apoptosis. However, after irradiation with ions, an anti-apoptotic function of survivin is not evident, possibly because of the serious damage produced by densely ionizing radiation.

The experimental measurement of the relative biological effectiveness of carbon ions with different qualities

The relative biological effectiveness (RBE) of carbon ions with linear energy transfer (LET) of 172 keV/mu m and 13.7 keV/mu m were determined in this study. The clonogenic survival and premature terminal differentiation were measured on normal human. broblasts AG01522C and NHDF after exposure of the cells to 250 kV X-rays and carbon ions with different qualities. RBE was determined for these two biological end points. The results showed that the measured RBE10 with a survival fraction of 10% was 3.2 for LET 172 keV/mu m, and 1.33 for LET 13.7 keV/mu m carbon ions. RBE for a doubling of post-mitotic. broblasts (PMF) in the population was 2.8 for LET 172 keV/mu m, and 1 for LET 13.7 keV/mu m carbon ions. For the carbon ion therapy, a high RBE value on the Bragg peak results in a high biological dose on the tumour. The tumour cells can be killed effectively. At the same time, the dose on healthy tissue would be reduced accordingly. This will lighten the late effect such as fibrosis on normal tissue.

Biodosimetry estimate for high-LET irradiation

The purpose of this paper is to prepare for an easy and reliable biodosimeter protocol for radiation accidents involving high-linear energy transfer (LET) exposure. Human peripheral blood lymphocytes were irradiated using carbon ions (LET: 34.6 keV mu m(-1)), and the chromosome aberrations induced were analyzed using both a conventional colcemid block method and a calyculin A induced premature chromosome condensation (PCC) method. At a lower dose range (0-4 Gy), the measured dicentric (dics) and centric ring chromosomes (cRings) provided reasonable dose information. At higher doses (8 Gy), however, the frequency of dics and cRings was not suitable for dose estimation. Instead, we found that the number of Giemsa-stained drug-induced G2 prematurely condensed chromosomes (G2-PCC) can be used for dose estimation, since the total chromosome number (including fragments) was linearly correlated with radiation dose (r = 0.99). The ratio of the longest and the shortest chromosome length of the drug-induced G2-PCCs increased with radiation dose in a linear-quadratic manner (r = 0.96), which indicates that this ratio can also be used to estimate radiation doses. Obviously, it is easier to establish the dose response curve using the PCC technique than using the conventional metaphase chromosome method. It is assumed that combining the ratio of the longest and the shortest chromosome length with analysis of the total chromosome number might be a valuable tool for rapid and precise dose estimation for victims of radiation accidents.

Survival and initial chromatid breakage in normal and tumour cells exposed in vitro to gamma rays and carbon ions at the HIRFL

Human hepatoma and normal liver cells were irradiated with C-12(6+) ion beams (linear energy transfer (LET) = 96 keV mu m(-1)) and gamma-rays at the Heavy Ion Research Facility in Lanzhou (HIRFL). The numbers and types of chromatid breaks were detected using the premature chromosome condensation technique. Irradiation with C-12(6+) ions produced a majority of isochromatid break types, while chromatid breaks were dominant for irradiation with gamma-rays. Experimental results showed that the initial level of chromatid breaks is clearly related to the absorbed dose from C-12(6+), ions and gamma-rays. The (12)C(6+)ions are relatively more effective at inducing initial chromatid breaks when compared with the gamma-rays. A relative biological effectiveness (RBE) of about 2.5 resulted for the induction of initial chromatid breaks by C-12(6+) ions relative to gamma-rays in both cell lines.

Melting of Au and Al in nanometer Fe/Au and Fe/Al multilayers under swift heavy ions: A thermal spike study

Knowing that Fe is sensitive to swift heavy ion irradiations whereas Au and Al are not, the behavior of nanometric metallic multilayer systems, like [Fe(3 nm)/Au(x)](y) and [Fe(3 nm)/Al(x)](y) with x ranging between 1 and 10 mn, were studied within the inelastic thermal spike model. In addition to the usual cylindrical geometry of energy dissipation perpendicular to the ion projectile direction, the heat transport along the ion path was implemented in the electronic and atomic sub-systems. The simulations were performed using three different values of linear energy transfer corresponding to 3 MeV/u of Pb-208, Xe-132 and Kr-84 ions. For the Fe/Au system, evidence of appearance of a molten phase was found in the entire Au layer, provided the Au thickness is less than 7 nm and 3 nm for Pb and Xe ions, respectively. For the Fe/Al(x) system irradiated with Pb ions, the Al layers with a thickness less than 4 nm melt along the entire ion track. Surprisingly, the Fe layer does not melt if the Al thickness is larger than 2 nm, although the deposited energy surpasses the electronic stopping power threshold of track formation in Fe. For Kr ions melting does not occur in any of the multilayer systems.

SEU ground and flight data in static random access memories

This paper presents the vulnerabilities of single event effects (SEEs) simulated by heavy ions on ground and observed oil SJ-5 research satellite in space for static random access memories (SRAMs). A single event upset (SEU) prediction code has been used to estimate the proton-induced upset rates based oil the ground test curve of SEU cross-section versus heavy ion linear energy transfer (LET). The result agrees with that of the flight data.