Enhanced cycling performance and high energy density of LiFePO4 based lithium ion batteries

LiFePO4 attracts a lot of attention as cathode materials for the next generation of lithium ion batteries. However, LiFePO4 has a poor rate capability attributed to low electronic conductivity and low density. There is seldom data reported on lithium ion batteries with LiFePO4 as cathode and graphite as anode. According to our experimental results, the capacity fading on cycling is surprisingly negligible at 1664 cycles for the cell type 042040. It delivers a capacity of 1170 mAh for 18650 cell type at 4.5C discharge rate. It is confirmed that lithium ion batteries with LiFePO4 as cathode are suitable for electric vehicle application. (c) 2007 Elsevier B.V. All rights reserved.

High energy ion implantation enhanced intermixed quantum well structures and their absorption characteristics in passive optical waveguides

We have shown that high energy ion implantation enhanced intermixing (HE-IIEI) technology for quantum well (QW) structures is a powerful technique which can be used to blue shift the band gap energy of a QW structure and therefore decrease its band gap absorption. Room temperature (RT) photoluminescence (PL) and guided-wave transmission measurements have been employed to investigate the amount of blue shift of the band gap energy of an intermixed QW structure and the reduction of band gap absorption, Record large blue shifts in PL peaks of 132 nm for a 4-QW InGaAs/InGaAsP/InP structure have been demonstrated in the intermixed regions of the QW wafers, on whose non-intermixed regions, a shift as small as 5 nm is observed. This feature makes this technology very attractive for selective intermixing in selected areas of an MQW structure. The dramatical reduction in band gap absorption for the InP based MQW structure has been investigated experimentally. It is found that the intensity attenuation for the blue shifted structure is decreased by 242.8 dB/cm for the TE mode and 119 dB/cm for the TM mode with respect to the control samples. Electro-absorption characteristics have also been clearly observed in the intermixed structure. Current-Voltage characteristics were employed to investigate the degradation of the p-n junction in the intermixed region. We have achieved a successful fabrication and operation of Y-junction optical switches (JOS) based on MQW semiconductor optical amplifiers using HE-IIEI technology to fabricate the low loss passive waveguide. (C) 1997 Published by Elsevier Science B.V.

Enhanced biological effect induced by a radioactive C-9-ion beam at the depths around its Bragg peak

To explore the potential of double irradiation source, radioactive C-9-ion beam, in tumor therapy, a comparative study oil the surviving effect of human salivary gland cells at different penetration depths between C-9 and C-12-ion beams has been carried out. The 9C-ion C beam, especially at the distal side of the beam came out more efficient in cell killing at the depths around its Bragg peak than the 12 Bragg peak. Compared to the C-12 beam, an increase in RBE by a factor of up to 2.13 has been observed at the depths distal to the Bragg peak of the 9C beam. The 9C beam showed an enhanced biological effect at the penetration depths around its Bragg peak, corresponding to the stopping region of the incident C-9-ions and where the delayed low-energy particles were emitted. Further analysis revealed that cell lethality by the emitted particles from the stopping C-9-ions is responsible for the excessive biological effect at the penetration depths around the Bragg peak of the C-9 beam.

Bubble regime for ion acceleration in a laser-driven plasma

Proton trapping and acceleration by an electron bubble-channel structure in laser interaction with high-density plasma is investigated by using three-dimensional particle-in-cell simulations. It is shown that protons can be trapped, bunched, and efficiently accelerated for appropriate laser and plasma parameters, and the proton acceleration is enhanced if the plasma consists mainly of heavier ions such as tritium. The observed results are analyzed and discussed in terms of a one-dimensional analytical three-component-plasma wake model.

Low-loss planar and stripe waveguides in Nd3+-doped silicate glass produced by oxygen-ion implantation

We report on the fabrication and characterization of low-loss planar and stripe waveguides in a Nd3+-doped glass by 6 MeV oxygen-ion implantation at a dose of 1x10(15) ions/cm(2). The dark mode spectroscopy of the planar waveguide was measured using a prism coupling arrangement. The refractive index profile of the planar waveguide was reconstructed from a code based on the reflectivity calculation method. The results indicate that a refractive index enhanced region as well as an optical barrier have been created after the ion beam processing. The near-field mode profiles of the stripe waveguide were obtained by an end-fire coupling arrangement, by which three quasitransverse electric modes were observed. After annealing, the propagation losses of the planar and stripe waveguides were reduced to be similar to 0.5 and similar to 1.8 dB/cm, respectively. (c) 2007 American Institute of Physics.

Low loss waveguide in Nd3+-doped silicate glass fabricated by carbon ion implantation

Low loss index enhanced planar waveguides in Nd3+-doped silicate glass were fabricated by 3.0 MeV C+ ion implantation. The enhancement of the refractive index confined the light propagating in the waveguide. The prism-coupling method was used to measure dark modes in the waveguide. The effective refractive indices of the waveguide were obtained based on the dark modes. The moving fiber method was applied to measure the waveguide propagation loss. Loss measured in non-annealed samples is about 0.6 dB/cm. And the waveguide mode optical near-field output at 633 nm was presented. (c) 2005 Elsevier B.V. All rights reserved.

Property studies of optical waveguide formed by 6.0 MeV carbon ion implantation into Nd : silicate glass

Nd:silicate glass was implanted at room temperature by 6.0 MeV C3+ ions with a dose of 2.0 x 10(15) ions cm(-2). A waveguide with thickness of about 6.3 mu m was formed. The prism-coupling method was used to observe the dark modes of the waveguide at 633 nm and 1539 nm, respectively. There are three dark modes at 633 nm, of which one is the enhanced-index mode. The propagation loss of the enhanced-index mode in the waveguide measured at 633 nm is 0.42 dB cm(-1) after annealing at 217 degrees C for 35 min. The reflectivity calculation method was applied to simulate the refractive index profiles in the waveguide. The mode optical near-field output at 633 nm was presented.

GaInNAs/GaAs multiple-quantum well resonant-cavity-enhanced photodetectors at 1.3 mu m

A GaInNAs/GaAs multiple quantum well (MQW) resonant-cavity enhanced photodetector (RCF-PD) operated at a wavelength of 1.3 mum with the full width at half maximum of 4nm has been demonstrated. The GaInNAs RCE - PD was grown by molecular beam epitaxy using a homemade ion-removed dc plasma cell as a nitrogen source. GaInNAs/GaAs MQW shows a strong exciton peak at room temperature, which is very beneficial for applications in long-wavelength absorption devices. For a 100 mum diameter RCE-PD, the dark current is 20 and 32 pA at biases of 0 and 6 V, respectively, and the breakdown voltage is - 18 V. The measured 3 dB bandwidth is 308 MHz, which is limited by the resistance of p-type distributed Bragg reflector mirror. The tunable wavelength in a range of 18 nm with the angle of incident light was observed.

Influence of ion energy and deposition temperature on the surface morphology of carbon films deposited by ion beams

Carbon films were deposited by mass-selected ion beam technique with ion energies 50-200eV at a substrate temperature from room temperature to 80 degreesC,. For the energies used, smooth diamond-like carbon films were deposited at room temperature. When the substrate temperature was 600 degreesC,rough graphitic films were produced. But highly oriented carbon tubes were observed when the energies were larger than 140eV at 800 degreesC. They were perpendicular to the surface and parallel to each other. preferred orientation of graphite basic plane was observed by high-resolution electron microscopy. Shallow ion implantation and stress are responsible for this orientation.

Effect of ion-induced damage on GaNAs/GaAs quantum wells grown by plasma-assisted molecular beam epitaxy

The effect of ion-induced damage on GaNAs/GaAs quantum wells (QWs) grown by molecular beam epitaxy employing a DC plasma as the N source was investigated. Ion-induced damage results in: (i) an observed disappearance of pendellosung fringes in the X-ray diffraction pattern of the sample; (ii) a drastic decrease in intensity and a broadening in the full-width at half-maximum of photoluminescence spectra. It was shown that ion-induced damage strongly affected the bandedge potential fluctuations of the QWs. The bandedge potential fluctuations for the samples grown with and without ion removal magnets (IRMs) are 44 and 63 meV, respectively. It was found that the N-As atomic interdiffusion at the interfaces of the QWs was enhanced by the ion damage-induced defects. The estimated activation energies of the N-As atomic interdiffusion for the samples grown with and without IRMs are 3.34 and 1.78 eV, respectively. (C) 2001 Elsevier Science B.V. All rights reserved.

Ion bombardment as the initial stage of diamond film growth

It is believed that during the initial stage of diamond film growth by chemical-vapor deposition (CVD), ion bombardment is the main mechanism in the bias-enhanced-nucleation (BEN) process. To verify such a statement, experiments by using mass-separated ion-beam deposition were carried out, in which a pure carbon ion beam, with precisely defined low energy, was selected for investigating the ion-bombardment effect on a Si substrate. The results are similar to those of the BEN process, which supports the ion-bombardment-enhanced-nucleation mechanism. The formation of sp(3) bonding is based on the presumption that the time of stress generation is much shorter than the duration of the relaxation process. The ion-bombarded Si is expected to enhance the CVD diamond nucleation density because the film contains amorphous carbon embedded with nanocrystalline diamond and defective graphite. (C) 2001 American Institute of Physics.

Carbon film deposited by mass-selected low energy ion beam technique and ion bombardment effect

By mass-selected low energy ion beam deposition, amorphous carbon film was obtained. X-ray diffraction, Raman and Auger electron spectroscopy depth line shape measurements showed that such carbon films contained diamond particles. The main growth mechanism is subsurface implantation. Furthermore, it was indicated in a different way that ion bombardment played a decisive role in bias enhanced nucleation of chemical vapor deposition diamond.

Correlation of electrical and optical properties in dually Cd+ and N+ ion-implanted GaAs

Cd in GaAs is an acceptor atom and has the largest atomic diameter among the four commonly-used group-II shallow acceptor impurities (Be, Mg, Zn and Cd). The activation energy of Cd (34.7 meV) is also the largest one in the above four impurities, When Cd is doped by ion implantation, the effects of lattice distortion are expected to be apparently different from those samples ion-implanted by acceptor impurities with smaller atomic diameter. In order to compensate the lattice expansion and simultaneously to adjust the crystal stoichiometry, dual incorporation of Cd and nitrogen (N) was carried out into GaAs, Ion implantation of Cd was made at room temperature, using three energies (400 keV, 210 keV, 110 keV) to establish a flat distribution, The spatial profile of N atoms was adjusted so as to match that of Cd ones, The concentration of Cd and N atoms, [Cd] and [N] varied between 1 x 10(16) cm(-3) and 1 x 10(20) cm(-3). Two type of samples, i.e., solely Cd+ ion-implanted and dually (Cd+ + N+) ion-implanted with [Cd] = [N] were prepared, For characterization, Hall effects and photoluminescence (PL) measurements were performed at room temperature and 2 K, respectively. Hall effects measurements revealed that for dually ion-implanted samples, the highest activation efficiency was similar to 40% for [Cd] (= [N])= 1 x 10(18) cm(-3). PL measurements indicated that [g-g] and [g-g](i) (i = 2, 3, alpha, beta,...), the emissions due to the multiple energy levels of acceptor-acceptor pairs are significantly suppressed by the incorporation of N atoms, For [Cd] = [N] greater than or equal to 1 x 10(19) cm(-3), a moderately deep emission denoted by (Cd, N) is formed at around 1.45-1.41 eV. PL measurements using a Ge detector indicated that (Cd, N) is increasingly red-shifted in energy and its intensity is enhanced with increasing [Cd] = [N], (Cd, N) becomes a dominant emission for [Cd] = [N] = 1 x 10(20) cm(-3). The steep reduction of net hole carrier concentration observed for [Cd]/[N] less than or equal to 1 was ascribed to the formation of (Cd, N) which is presumed to be a novel radiative complex center between acceptor and isoelectronic atoms in GaAs.