and two extreme cathode voltages, 500 and 1000 V 共dis- charge cannot be ignited below 500 V, and due to the limi- tation of the mass spectrometer to ionenergy below 1000 eV, 1000 V corresponds to the maximum energy that we can measure兲. When the cathode bias voltage is at 1 kV, the discharge pressure is limited by the Paschen curve to a range from 30 to 70 mTorr. For this pressure range the num- ber of collisions inside the sheath remains constant 共s / re- mains constant兲. The decrease of the mean free path at higher pressure is compensated by the decrease of the sheath thick- ness due to plasma density increase at higher pressure. Con- sequently, minor changes in the shape of the IED are ex- pected. When a lower bias voltage is used 共0.5 kV兲, the discharge can be operated under a large range of pressures from 75 to 250 mTorr. Within this pressure range, the num- ber of collision increases from 6.9 to 10.3, thus causing sig- nificant changes in the IED. This is in agreement with our experimental observations.
Concerning the ionenergy balance, the ion temperature profiles are simulated including: 1/ a best fit to the passive measured spectra of each analyser, 2/ for all the analysers, the same normalisation factor for the neutral density profile (fast computed consistently with ion temperature[ 2 ]) and 3/ the consistency with neutron yield and plasma composition. Standard diagnostics provide the other experimental data required in the simulation code (ne(r), Te(r), Zeff, neutron yield and plasma geometry). A 4-step electron density scan is performed on a 4 s, 4 MW ICRH pulse (f = 57.4 MHz, dipole phasing), launched in a mainly deuterium plasma (n D /n He 2, B = 3.9 T, Ip=1.3 MA). Electron and ion kinetic thermal energies are shown on figure 1. In the ohmic phase, diamagnetic and kinetic energy are found in good agreement. The lowest density point corresponds to a monster sawtooth. For the other points, data are averaged during 100 ms (about two normal sawteeth). If we assume that perpendicular supra-thermal ionenergy content is the difference between diamagnetic and thermal kinetic energy, it is within the error bars for the high density point, but clearly increases with decreasing density. The thermal energy content has also been evaluated on a 4 MW pulse of FWCD (f = 47.7 MHz, co-current phasing) launched in mainly helium plasma (n D /n He 0.7, B = 2.2 T, Ip = 0.76 MA). It is
IONENERGY DISTRIBUTION OF N 2+ FROM N 2 ANDO 2+ FROM O 2 .
R. LOCHT, J. MOMIGNY
Institut de Chimie, Université de Liège, Sart-Tilman par Liège I- Belgium
The formation of N 2+ ions by electron and ion impact has been investigated by several groups (1-1). The lowest threshold for the appearance energy is measured at around 61 eV (1, 2) and 54 eV (3). The N 2+ ionenergy distribution has been examined as a function of the electron energy and the angle between ion and electron beam (1-3). No thermal peak has been observed. The present contribution will report preliminary results on N 2+ from N 2 and O
We have used observations of the ionenergy spectra using the Equator-S satellite to test the validity of two models of the storm-time convection electric ®eld. This is the ®rst time that the Weimer model has been tested for its validity in the equatorial plane using drift trajectories. We ®nd that assuming convection in a Volland-Stern electric ®eld with charge exchange as the only loss mechanism results in predicted losses that are larger than observed. This was evident in both the predicted energy spectra and the predicted pitch angle distributions. This is in agreement with the ®ndings of Jordanova et al. (1999) from comparisons with POLAR data. Chen et al. (1998) in comparing simulating pitch angle distributions with CRRES data for higher energy ions (>50 keV/e) found the opposite result. Assuming convection in the Weimer ®eld gives signi®cantly better agreement with the magnitude of the losses observed. From comparisons of the drift paths, this is primarily because the Volland-Stern trajectories in the transition region go much closer to the Earth. The dierences in charge exchange cross sections of H + and O + at these
IEDF, versus the retarding potential, V R , which is equivalent to the ionenergy for singly charge ions, and radius.
The magnitude of the derivative of the current for Fig. 7(b) is a factor of 10 lower than for Fig. 7(d). The plot of
dI C /dV R for each radius was analyzed for the three values of V min , V max , and V p , as illustrated in Fig. 5(a). The
minimum and maximum potentials at each radius are shown by solid lines, while the average potential is shown as a
The method developed here to determine the initial energy and angular distribution function (NIEADF) of NI emitted from the sample surface in H 2 plasma is validated by a good agreement of the model with the experiment. Indeed, using SRIM distribution function as initial NIEADF, the model can reproduce the Negative-IonEnergy Distribution Functions (NIEDFs) measured by the mass spectrometer at different tilt angles of the sample. Moreover, we showed by tilting the sample that this validation concerns the whole distribution of emitted ions in terms of energy and angle. It confirms that the NIEADF for HOPG is close to the neutral distribution function given by SRIM. It implies that the NI formation probability on the graphite surface, under the present experimental conditions, is almost independent of the angle and energy of emission as stated previously 47 . The present paper shows that only a small part of the negative- ions emitted by the sample is collected by the mass spectrometer and one measurement at one particular tilt angle is not enough to characterize negative-ion yield. Furthermore, the model shows that hydrogenated materials will probably present high negative ion signal at 0° tilt angle contrary to non-hydrogenated materials. Therefore, in order to analyze efficiency of different negative-ion enhancer materials, it is of primary importance to compare the corresponding NI yields at different tilt angles. The best approach is to use SRIM to compute NIEADF on the sample surface and to validate it by comparison with experimental NIEDF measured at different tilt angles. In that way, the NIEADF of ions emitted by different materials can be directly compared.
Pilling et al. 2010a ,b; Dartois et al. 2013 ). We conclude that in our selected ice mixture where both components, methanol and ammonia, are dissociated easily by vacuum-UV photons, similar photon and ionenergy doses led to similar chemical reactions, based on the similarity of the IR spectra of the processed ices. In general, it is therefore not possible to use simple astrophysical molecules (detected in ice mantles or in the gas phase, toward, for instance, hot cores or the higher temperature regions in a pro- tosolar nebula disk, where ice mantles sublimate) as tracers of either UV or ion irradiation. Even the direct dissociation of the most stable molecules such as N 2 or CO in the ice, which can-
8(b) . This is in good agreement with the time-resolved mea- surement of the ion flux in no-bias conditions in Sec. III and might open the possibility to reduce surface damage caused by high energy ions. It is important to underline that although the high energy flux is strongly reduced, for a given RF biasing power the ionenergy of this flux is multiplied by more or less a factor of 5 when the plasma is pulsed at 20% duty cycle. It follows that when the plasma is pulsed under our typical etching conditions at this duty cycle (with 750 W source and 200 W bias), the ionenergy is estimated to be about 2.5 keV, leading to very specific etching conditions compared to what can be obtained in a CW plasma. Indeed, since the wafer is bombarded by a low flux of very energetic ions, we are in a condition that resembles those obtained in purely capacitively coupled reactors, but at lower pressure with collisionless sheaths and with a high flux of low energy ions during the off-time of the plasma pulses.
The presence of the β phase at this low temperature may be due to local constraints induced by the ion irradi- ation. Past experimental and theoretical studies on ion– matter interaction show that, at this ionenergy regime, collision cascades can lead to the formations of spatially localized regions rich in interstitial atoms or vacancies [37, 54–56]. Interstitial-rich regions could cause an in- crease of the local high internal pressure favoring the presence of the β phase that is characterized by a volume 2% larger than the α phase. In connection to the persis- tence of small β-phase regions, the sample magnetization is expected to be reduced with respect to the reference sample, which is the case as visible in the magnetome- try measurements in Fig. 1. At very low temperature (T = 100 K) not monitored with the MFM, irradiated samples have practically the same saturation magneti- zation than pristine samples  suggesting that these “frozen” β-phase regions are thus suppressed.
The carbonyl groups were intermediate states and could oxygen saturate, transforming to carboxyl groups, helping to explain the relative stability in carbonyl concentration and large increase in –COOH in the C1s peak from 5 to 10 min. This process would be kinetically dependent on the rate of damage site and hole formation (i.e., new dangling bond creation rate), and was also reflected in the ionenergy study (Figure 7 b). As the ion kinetic energy increased there was a steady decrease in epoxide concentration, primarily because at higher energies there is an increased chance of damaging the lattice and so inserting oxygen as other (carbonyl or carboxyl) forms. The slight decrease in the sp 3 -C component observed when the sample was irradiated with 0.1 keV ions could be associated to a preferential removal of physically adsorbed species (amorphous carbon and oxygen species including water) occurring during the synthesis and due to the exposure to ambient air.
spectrograms of H + , He + , He ++ , O + . The energy/charge ra-
tios of the ion populations seems to be quite similar to those of their masses. This can be appreciated in Fig. 4 which displays the four ionenergy spectra at a chosen time dur- ing the ion dispersion (07:40:37 UT). The vertical gray areas indicate the energies which correspond to a energy/charge ratio equal to the mass ratio based on the energy of the flux maximum of the hydrogen energy spectra which corresponds to a velocity of 350 km/s. The agreement between expecta- tions and observations is reasonably good. This observation strongly suggest that the ionospheric ions precipitating inside the cusp have first reached the magnetosheath with a weak kinetic energy and have been accelerated there up to a veloc- ity close to the magnetosheath velocity and then re-enter the magnetosphere inside the high-latitude cusp.
Typically, supercapacitors and batteries differ in electrochemical mechanisms, hence featuring almost opposite energy and power characteristics 5 – 8 . However, the demand for power and energy
supply is equally imperative in actual use and is keen to expand in the future. Thus it is highly desirable to design new electro- chemical energy storage technologies to mitigate the trade-off between power density and energy density 9 . Recently, the dual- ionenergy storage (DIES) concept has attracted increasing attention as it holds different charge storage chemistry with the conventional “rocking-chair” mechanism 10 – 13 . In DIES devices, the electrolyte provides both cations and anions to be involved in charge storage. Graphitic carbon provides an ideal host for anion accommodation. The high anion-intercalating potential (>4.0 V vs. Li/Li + ) and ultrafast rate capability (78% capacity retention, up to 100 C rate) enable graphitic carbon a promising cathode for constructing energy storage devices with both high energy and power densities 14 . Previous studies have proposed several new DIES devices by assembling graphite cathode with conventional battery-type anodes (such as Li metal 14 , graphite 15 , Al metal 16 , Sn
T riggered by a huge energy demand from various industries ranging from individual electronics to grid storage, elec- trochemical energy storage devices represent an active ﬁeld for both research development and practical applications 1 – 4 . Typically, supercapacitors and batteries differ in electrochemical mechanisms, hence featuring almost opposite energy and power characteristics 5 – 8 . However, the demand for power and energy supply is equally imperative in actual use and is keen to expand in the future. Thus it is highly desirable to design new electro- chemical energy storage technologies to mitigate the trade-off between power density and energy density 9 . Recently, the dual- ionenergy storage (DIES) concept has attracted increasing attention as it holds different charge storage chemistry with the conventional “rocking-chair” mechanism 10 – 13 . In DIES devices, the electrolyte provides both cations and anions to be involved in charge storage. Graphitic carbon provides an ideal host for anion accommodation. The high anion-intercalating potential (>4.0 V vs. Li/Li + ) and ultrafast rate capability (78% capacity retention, up to 100 C rate) enable graphitic carbon a promising cathode for constructing energy storage devices with both high energy and power densities 14 . Previous studies have proposed several new DIES devices by assembling graphite cathode with conventional battery-type anodes (such as Li metal 14 , graphite 15 , Al metal 16 , Sn metal 17 , WS 2 18 , etc.). However, the power performance of DIES devices is still limited, and there is great interest in designing high-rate pseudocapacitive anode to be combined with graphite cathode to assemble high-energy, high-power DIES device.
3. School of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
We have investigated the use of aluminum based amorphous metallic glass as the anode in lithium ion rechargeable batteries. Amorphous metallic glasses have no long-range ordered microstructure; the atoms are less closely packed compared to the crystalline alloys of the same compositions; they usually have higher ionic conductivity than crystalline materials, which make rapid lithium diffusion possible. Many metallic systems have higher theoretical capacity for lithium than graphite/carbon; in addition irreversible capacity loss can be avoided in metallic systems. With careful processing, we are able to obtain nano-crystalline phases dispersed in the amorphous metallic glass matrix. These crystalline regions may form the active centers with which lithium reacts. The surrounding matrix can respond very well to the volume changes as these nano-size regions take up lithium. A comparison study of various kinds of anode materials for lithium rechargeable batteries is carried out.
a Pesquisa do Estado de S˜ ao Paulo (Brazil), Natural Sci- ence Foundation of China (People’s Republic of China), Croatian Science Foundation and Ministry of Science and Education (Croatia), Ministry of Education, Youth and Sports (Czech Republic), Centre National de la Recherche Scientifique, Commissariat ` a l’ ´ Energie Atom- ique, and Institut National de Physique Nucl´ eaire et de Physique des Particules (France), Bundesministerium f¨ ur Bildung und Forschung, Deutscher Akademischer Aus- tausch Dienst, and Alexander von Humboldt Stiftung (Germany), J. Bolyai Research Scholarship, EFOP, the New National Excellence Program ( ´ UNKP), NKFIH, and OTKA (Hungary), Department of Atomic Energy and Department of Science and Technology (India), Israel Science Foundation (Israel), Basic Science Research Pro- gram through NRF of the Ministry of Education (Korea), Physics Department, Lahore University of Management Sciences (Pakistan), Ministry of Education and Science, Russian Academy of Sciences, Federal Agency of Atomic Energy (Russia), VR and Wallenberg Foundation (Swe-
This microscope is equipped with a field- emission cathode and a parallel Gatan 666 EELS spectrom- eter. The EELS spectra were recorded over the first 50 eV on each image point of the specimen 共typically 256⫻256兲. The EELS experiment is performed in the low-energy-loss do- main. Plasmons, corresponding to plasma oscillations of va- lence electrons associated with each phase of the analyzed area, are the major signatures in this energy domain of the EELS spectra. Bulk silicon and silica plasmons are located at 17 and 23.5 eV, respectively. They are well separated and thus can be used to get the image associated with the corre- sponding phase. After acquisition of a spectrum at each point of the image, contributions from silicon plasmon and silica plasmon are isolated by reconstruction of the signal with reference spectra of Si and silica. Then a map can be dis- played where the gray levels are defined by the weight of Si deduced from the reconstruction parameters. On such “chemical images,” all the Si NCs are visible, amorphous, eith crystalline, and in the last case whatever their orientation is. A contrast enhancement method is applied to these images in order to perform quantitative measurements such as the NC mean size and aerial density and surface fraction and number of atoms stored within the NCs. In order to control the homogeneity of the NC distribution throughout the plan- view TEM samples, energy filtering transmission electron microscopy 共EFTEM兲 experiments have also been performed for particular samples. By inserting an energy-selecting slit in the energy-dispersive plane of the filter at the Si plasmon energy, the population of Si NCs can also be visualized. A TEM-FEG microscope, Tecnai F20ST equipped with an en- ergy filter, TRIDIEM from Gatan was used. The contrast in
We deduced the mean energy absorbed per second in the liquids from the energy spectra and event rates computed by Monte Carlo simulation. Systematic uncertainty estimation takes into account uncertainties related to : (i) the height of active volume depending on tin wire gaskets thickness after compression, (ii) the radius of active volume due to engineering tolerance of manufactured parts of the ionization chamber, (iii) the radioactive source positioning. In addition, owing to the geometry of the ionization chamber, electric field lines in the active volume of liquid are slightly diverted. The signal created in these regions, representing approximately 5 % of volume, may be loss. According to the simulation, the mean energy deposited in these regions is 5.0 ± 0.2 MeV/s in TMSi and 32.8 ± 0.9 MeV/s in TMBi and is taken into account in the final result as a systematic uncertainty. The mean energy absorbed per second was then found to be 124 +4 −6 MeV/s in TMSi and 720 +19 −38 MeV/s in TMBi. One should notice that the energy absorbed in TMBi is almost 6 times higher than in TMSi. This is the consequence of the high density and high photo-electric efficiency of TMBi.