Increasing Ion Energy Research Articles

Measurement of Ion Energy Distribution in a Cylindrical Inertial Electrostatic Confinement Fusion (C-IECF) Device

In recent researches, an assisted glow discharge experiment using an external ion source has been tried to reduce operation gas pressure. As results, operating gas pressure has been successfully reduced from 1.5 Pa to 0.3 Pa, and the neutron production rate has increased.These results are considered to be due to an increase of ion energy. However, it is necessary to measure the ion energy distribution of the Cylindrical Inertial Electrostatic Confinement Fusion (C-IECF) device in order to confirm this. To do this, we have measured the distribution of the neutral particle beam energy (relative to ion energy distribution). These experimental results demonstrate that a decrease of operation gas pressure (from 1.7 Pa to 0.3 Pa) contributes to the increase in ion energy.

Nanopatterning of Si(110) surface by ion sputtering: An experimental and simulation study

Nanopatterning of Si(110) surface by the normal incident ${\mathrm{Ar}}^{+}$ ion sputtering has been conducted as a function of sample temperature (room temperature---$800\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$) and ion energy $(1--5\phantom{\rule{0.3em}{0ex}}\mathrm{keV})$ with the ion flux of $20\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{A}∕{\mathrm{cm}}^{2}$. The surface morphology was characterized by an atomic force microscope. For ion energy of $1.5\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$, the sputtered surface morphology changes from a dim dot/hole pattern to a distinct dot one with the increasing temperature. On the other hand, at the temperature of $800\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, the nanodot shape of the dot pattern evolves from being $\text{circular}\ensuremath{\rightarrow}\text{elliptical}\ensuremath{\rightarrow}\text{circular}\ensuremath{\rightarrow}\text{elliptical}$ with the increasing ion energy in general. A dynamic continuum model is adopted to describe the experimental results, which includes both the Bradley--Harper (BH) mechanism good for the amorphous surface under ion sputtering and the Ehrlich--Schwoebel (ES) one for the crystalline surface. By adjusting the effective surface tension following its temperature- or ion energy-dependence relationship in the BH or ES mechanism-relevant regime, the processes of surface morphology evolution have been simulated, which agrees with the experimental ones.

He + scattering on clean and oxygen covered Al(1 1 1)

We present results of a study of He + neutralisation on clean and oxygen covered Al(1 1 1). For clean Al(1 1 1) we find a small ion fraction which rapidly increases with increasing ion energy attaining about (0.4 ± 0.1)% at 4 keV. The overall behaviour is quite different from that observed on previously studied Ag surfaces and is attributed to reionisation processes, a conclusion supported by measurements using He atoms. When O 2 is adsorbed onto Al(1 1 1) at room temperature, we observe a rapid increase in the ion fraction, which attains a broad plateau for exposures higher than about 50 L. Experiments with incident He atoms lead to an ion fraction that is smaller, indicating that in this case a substantial fraction of ions is due to survival of incident ions. We attribute these changes to a decrease of the Auger neutralisation rates on the oxidic surface.

Determination of the thickness and density of the ion bombardment induced altered layer in SiC by means of reflection electron energy loss study

The steady state surfaces of ion bombarded 3C-, 4H- and 6H-SiC samples were studied by means of reflected electron energy loss spectroscopy (REELS). The REELS exhibit a well-defined loss peak in the region of about 20 eV. The position of the maximum of the loss peak depends on the bombarding ion energy (decreasing with increasing ion energy), and on the primary electron beam energy (increasing with increasing primary energy). This behavior can be explained if we suppose that the plasmon energy in the altered layer (produced by ion bombardment) is different from that of the unaltered bulk. In this case the measured loss peak is the sum of two overlapping plasmon peaks. With modeling the system as a homogeneous altered layer and a homogeneous unaltered substrate the plasmon energy in the altered layer was derived to be 19.8 eV. The large change of the plasmon energy with respect to the bulk value of 23 eV is explained by a thin low density overlayer on the surface of the sample produced by the ion bombardment.

Structure and Chemical Bonds of CNx Films Deposited by Alternating Irradiations of Mass-Separated Ion Beams of C+ and N+

Carbon nitride films were prepared on Si(100) wafers by alternating irradiations of mass-separated low-energy ion beams of C+ and N+ at an ultra-high vacuum pressure of 10-7 Pa. The dependences of the ion energy and transport ratios of carbon ions to nitrogen ions on the film structure and chemical bonds formed were investigated. The graphite-like film, which was prepared at an ion energy of 30 eV and a transport ratio of 1/1, has a highly preferential crystal orientation. The graphite basal plane is curved and interlinked, and the c-axis of the graphite basal plane is parallel to the film growth surface. This highly preferential crystal orientation changed to a random orientation with increasing ion energy up to 200 eV due to increasing number of sp2-hybridization C–N bonds. The ratio of the number of sp2 C–N to the number of sp3 C–N bonds also changed with ion transport ratio, and a new phase with a lattice spacing of 0.204 nm formed with increasing the sp3/sp2 number ratio.

Carbonization of polyimide by swift heavy ion irradiations: Effects of stopping power and velocity

We have studied the carbonization of polyimide Kapton-H (pyromellitic dianhydride-oxydialinine, PMDA-ODA) thin films under heavy ion irradiations in the electronic slowing down regime. Irradiations were performed with 650-MeV Ni, 843-MeV Xe, 2.6-GeV Xe, 1.1-GeV Ta, and 707-MeV Pb ions that were transmitted through the polymer films with the electronic stopping power ranging between 3.5 and 17 keV nm −1. Room-temperature ac/dc electrical conductivity measurements, together with ESR, UV–visible optical absorption, and micro-Raman spectroscopy were used to characterize the irradiated films. These new data are compared to our previous results obtained with heavy ion irradiations in the 1-MeV uma −1 energy range. At the largest fluences near 10 13 cm −2 the resulting carbonaceous material is found to be 8–9 orders of magnitude less conducting than with the slower ions. Such large dc-conductivity deviations are confirmed by the spin–lattice relaxation times deduced from the ESR line saturation measurements that are two orders of magnitude longer with the swift ions than with the slower ions. The evolution of the Raman spectra also shows that the appearance of a conjugated sp 2-bonded structure is delayed with respect to the slow ion case, and is probably incomplete in the observed fluence range. The yield of paramagnetic centers is found to decrease when the ion energy increases. This is interpreted by an ion-velocity effect on damage due to a dilution of the deposited energy in the ion tracks. We think that this also induces a smaller sp 2 cluster density impeding charge transport in the carbonaceous material.

Ion-Sputter-Induced Nanodots on Si(110): Ion EnergyDependence

Nanodot arrays were formed on Si(110) surface undernormal-incident Ar+ ion sputtering at substratetemperature of 800 degrees C. The ion flux was 20 μA/cm2, andthe ion energies were 1–5 keV. The surface was imaged by an atomic forcemicroscope (AFM). It was found that with the increasing ion energy, theaverage ellipticity of the dots changes in an oscillating manner;meanwhile the average dot size increases monotonously. Based on adynamic continuum model, and taking into consideration the asymmetry ofthe Ehrlich-Schwoebel diffusions along the ⟨100⟩ and⟨11̄0⟩ crystallographic directions, we carry out thesimulations, which reproduce the experimental results qualitatively.

Energy and fluence dependences of helium retention in stainless steel

Helium retention behavior of 316L stainless steel (316L SS) used for the first wall of the large helical device (LHD) was investigated by using an ECR plasma/ion apparatus and thermal desorption spectroscopy. Samples of 316L SS were irradiated by helium ions with different energy. After helium ion irradiation with 100s eV energy, the desorption temperature of the retained helium was below 800K. As increasing ion energy, the fraction of helium desorbed temperatures >800K gradually increased. The retained amount of helium saturated for ion fluences above 1.0×1017He/cm2. The retained amount of He was similar to that observed in other plasma facing materials. For irradiation fluences >1.0×1017He/cm2, blister formation was observed. The present results are consistent with the desorption behavior of 316L SS samples exposed to LHD plasmas.

Self-organized lamellar structured tantalum–nitride by UHV unbalanced-magnetron sputtering

The effect of crystal orientation and microstructure on the mechanical properties of TaNx was investigated. TaNx films were grown on a SiO2 substrate by ultrahigh vacuum unbalanced magnetron sputter deposition in mixed Ar/N2 discharges at 20 mTorr (2.67 Pa) and at 350 °C.Unlike the Ti–N system, in which TiN is the terminal phase, a large number of N-rich phases in the Ta–N system could lead to layers which had self-organized nanosized lamella structure of coherent cubic and hexagonal phases, with a correct choice of nitrogen fraction in the sputtering mixture and ion irradiation energy during growth. The preferred orientations and the microstructure of TaNx layers were controlled by varying incident ion energy Ei (=30–50 eV) and nitrogen fractions fN2 (=0.1–0.15). TaNx layers were grown on (0002)-Ti underlayer as a crystallographic template in order to relieve the stress on the films.The structure of the TaNx film transformed from B1-NaCl δ–TaNx to lamellar structured B1-NaCl δ-TaNx+ hexagonal ɛ-TaNx or B1-NaCl δ-TaNx+hexagonal γ-TaNx with increasing ion energy at the same nitrogen fraction fN2. The hardness of the films also increased by the structural change. At the nitrogen fraction of 0.1–0.125, the structure of the TaNx films was changed from δ-TaNx+ɛ-TaNx to δ-TaNx+γ-TaNx with increasing ion energy. However, at the nitrogen fraction of 0.15, the film structure did not change from δ-TaNx+ɛ-TaNx over the whole range of the applied ion energy. The hardness increased significantly from 21.1 to 45.5 GPa with increasing ion energy.

Nitrogen ion implanted nanostructured titania films used in dye-sensitised solar cells and photocatalyst

Nanostructured titania films were implanted with N at energies between 10 and 40 keV and ion dose range 10 14 to 5 × 10 16 cm −2 and the films were characterized using various techniques. The surface morphology of the nanostructured films has been modified with ion implantation as observed using scanning electron microscopy (SEM). From SIMS depth profile analysis the amount of nitrogen was found to increase with increasing ion energy. The profile of N appeared to have a skewed Gaussian curve and the results have been explained using SRIM theoretical simulations. A maximum nitrogen concentration of about 6.08 at% has been quantified by X-ray photoelectron spectrometer (XPS). Transmittance of the films decreases with increasing implantation energy and ion dose due to defects created by the ion implantation. Annealing can remove defects and thereby increase the transmittance of the films.

Effect of ion irradiation during deposition on the structure of alumina thin films grown by plasma assisted chemical vapour deposition

Alumina thin films were deposited on hot work tool steel AISI H11 at a growth temperature of 500 to 600 °C by plasma assisted chemical vapour deposition and were studied with respect to the structure and composition by X-ray diffraction and electron-probe microanalysis, respectively. The electrical power density at the cathode was varied from 2.7 to 6.6 W/cm2. Within the investigated process window the following characteristic phases could be identified: γ-alumina and α-alumina as well as mixtures thereof. The alumina phase formation was found to be strongly influenced by deposition temperature and electrical power density at the substrate. It is shown that constitution changes due to a reduction in substrate temperature can be avoided by increasing the electrical power density at the cathode, which leads to an increase in both ion flux and ion energy at the substrate surface.

Etching yield of SiO2 irradiated by F+, CFx+ (x=1,2,3) ion with energies from 250 to 2000 eV

Etching yields of SiO2 have been determined for F+, CFx+ (x=1,2,3) ion irradiation with energy ranging from 250 to 2000 eV using a mass-analyzed ion-beam apparatus that can irradiate a single species ion to sample surfaces under an ultrahigh vacuum condition. The etching yield of CFx+ (x=1,2,3) was enhanced by the chemical effects of the ions, and both carbon and fluorine atoms from the incident ions were significant reactants. For lower energies, the etching yield increased with increasing ion energy. Above 1000 eV, the etching yield was gradually saturated with increasing ion energy. In the low ion energy region, steady etching did not occur, and an amorphous fluorinated carbon (a-C:F) film was deposited on the SiO2 surface. The ion energy region in which a-C:F film deposition occurred decreased with increasing fluorine atoms in incident CFx+ (x=1,2,3) ions.

Thin film growth using hyperthermal ions: a surface morphology study

Abstract Low-energy ion deposition and molecular beam epitaxy were used to systematically study the influence of the deposition energy on the growth of Co on Si(1 1 1). Co ions with a well-defined energy between 0.1 and 155 eV were deposited onto a 7 × 7 reconstructed Si surface, using sub- as well as supramonolayer coverage. For submonolayer coverage (0.3 ML), the initial periodicity degrades gradually with increasing ion energy: while for low energies (∼10 eV), 7 × 7 features remain clearly visible, these features disappear completely for higher deposition energies. In the supramonolayer (2 ML) region, we observe an increase in island density with increasing ion energy, which can be explained by the increasing amount of adatom–vacancy pairs and island breakup. Additionally, hyperthermal deposition yields a lower surface roughness compared to thermal deposition, with an optimal energy window for growing smooth films at ∼25 eV. This optimum can be attributed to enhanced layer-by-layer growth due to the extra energy provided by the incoming ion.

Effect of energetic ion irradiation on CdI2 films

The effect of energetic argon ion irradiation, using a 3.3 kJ pulsed plasma focus device, is studied systematically on a 4H polytype (002)-oriented CdI2 stoichiometric film having compressive residual stress. The CdI2 films were exposed to energetic ions from the plasma focus device at different distances from the top of the central electrode. The irradiation was found to change the orientation of the film to (110) at certain moderate irradiation distances. A linear decrease in grain size and residual stress was observed with decreasing irradiation distance (or increasing ion energy), consistent with both structural and morphological observations. The direct optical energy gap Eg was found to increase linearly at the rate 15 μeV/atm with the compressive stress. The combined data of present compressive stress and from earlier reported tensile stress show a consistent trend of Eg change with stress. The iodine–iodine distance in the unit cell could be responsible for the observed change in Eg with stress.

Advanced Coatings Through Pulsed Magnetron Sputtering

Pulsed magnetron sputtering (PMS) has become established as the process of choice for the deposition of dielectric materials for many applications. The process is attractive because it offers stable arc free operating conditions during the deposition of, for example, functional films on architectural and automotive glass, or antireflective/antistatic coatings on displays. Recent studies have shown that pulsing the magnetron discharge also leads to hotter and more energetic plasmas in comparison with continuous dc discharges, with increased ion energy fluxes delivered to the substrate. As such, the PMS process offers benefits in the deposition of a wide range of materials. The present paper describes three examples where PMS has led to either significant enhancement in film properties or enhanced process flexibility: in low friction titanium nitride coatings, in Al doped zinc oxide transparent conductive oxide coatings sputtered directly from powder targets and in thin film photovoltaic devices based on copper (indium/gallium) diselenide. These examples demonstrate the versatility of PMS and open up new opportunities for the production of advanced coatings using this technique. SE/499

Control of characteristic lengths for self-organized nanostructures of amorphouscarbon

We report the self-organized nanostructures of hydrogen-free amorphous carbon (a-C)with controllable characteristic length scales obtained by using ion beam assisteddeposition. By selecting various temperature regimes, two kinds of nanostructure,mounds and ripples, are successfully formed. For the growth temperature of200 °C, the fractal analysis of the surface shows that the lateral characteristic length formounding structures increases with increasing ion energy. But for ripple structures formedin the relatively high temperature region, the ripple wavelengths are found to show anonlinear dependence on the ion energy. Further, at certain temperatures thereexist energy thresholds for stopping the formation of ripple structures. Theseresults demonstrate that the characteristic scales of nanostructures for a-C can besignificantly controlled through the tuning ion energy in a well-defined manner.

Reactive physical vapor deposition of TixAlyN: Integrated plasma-surface modeling characterization

Reactive physical vapor deposition (RPVD) has been widely applied in the microelectronic industry for producing thin films. Fundamental understanding of RPVD mechanisms is needed for successful process development due to the high sensitivity of film properties on process conditions. An integrated plasma equipment-target nitridation modeling infrastructure for RPVD has therefore been developed to provide mechanistic insights and assist optimal process design. The target nitridation model computes target nitride coverage based on self-consistently derived plasma characteristics from the plasma equipment model; target sputter yields needed in the plasma equipment model are also self-consistently derived taking into account the yield-suppressing effect from nitridation. The integrated modeling infrastructure has been applied to investigating RPVD processing with a Ti0.8Al0.2 compound target and an Ar/N2 gas supply. It has been found that the process produces athermal metal neutrals as the primary deposition precursor. The metal stoichiometry in the deposited film is close to the target composition due to the predominance of athermal species in the flux that reaches the substrate. Correlations between process parameters (N2 flow, target power), plasma characteristics, surface conditions, and deposition kinetics have been studied with the model. The deposition process is characterized by two regimes when the N2 flow rate is varied. When N2 is dilute relative to argon, target nitride coverage increases rapidly with increasing N2 flow. The sputter yield and deposition rate consequently decrease. For less dilute N2 mixtures, the sputter yield and deposition rate are stable due to the saturation of target nitridation. With increasing target power, the electron density increases nearly linearly while the variation of N generation is much smaller. Target nitridation and its suppression of the sputter yield saturate at high N2 flow rendering these parameters insensitive to target power variation. The deposition rate, however, increases with target power as a result of the increased ion energy and flux at the target.

Transport properties of magnetic tunnel junctions with ion irradiated AlO barriers

The transport properties of magnetic tunnel junctions (Co - Fe/AlOx /Ni - Fe) with barriers irradiated by low energy Ar+ ions immediately after plasma oxidation of the aluminium film are investigated. The tunneling magnetoresistance is strongly reduced with increasing ion energies, whereas the area resistance product increases up to a factor 40 for ion energy up to 150 eV. At higher ion energy the resistance breaks down rapidly and the tunneling magnetoresistance vanishes completely. Structural alterations in the barrier are discussed. (C) 2003 Elsevier B. V. All rights reserved.

Helium Retention of 316L Stainless Steel Used for The First Wall of The Large Helical Device (LHD)

Helium retention of 316L stainless steel used for LHD plasma facing material was evaluated after helium ion irradiation by using a technique of thermal desorption spectroscopy (TDS). After the irradiation with helium energy of a few hundreds eV, most of the retained helium desorbed in the temperature range lower than 550°C. With increase of ion energy, the ratio of helium desorbed in higher temperature range (> 550°C) increased. In the irradiation with a helium energy of 3 keV, the retained helium desorbed only in the higher temperature range. Based upon the obtained results, the desorption behavior of helium in the stainless steel sample exposed to the LHD plasma discharges was discussed.

Temperature and bias-voltage dependent transport in magnetic tunnel junctions with low energy Ar-ion irradiated barriers

Magnetic tunnel junctions $({\mathrm{Mn}}_{83}{\mathrm{Ir}}_{17}{/\mathrm{C}\mathrm{o}}_{70}{\mathrm{Fe}}_{30}{/\mathrm{A}\mathrm{l}\mathrm{O}}_{x}{/\mathrm{N}\mathrm{i}}_{80}{\mathrm{Fe}}_{20})$ are investigated, whose barriers are irradiated by a low energy ${\mathrm{Ar}}^{+}$ ion beam immediately after plasma oxidation of the aluminum film. The tunneling magnetoresistance prior to irradiation is up to 71% at 10 K. The ion irradiation increases the area resistance product up to a factor of 40 for ion energies up to 150 V. Further, the tunneling magnetoresistance and the dielectric stability is strongly reduced with increasing ion energies. From the analysis of the temperature and the voltage dependence of the tunneling magnetoresistance we conclude that this is due to an irradiation induced local change of the coordination of the Al and O atoms in the barrier. This leads to a thicker barrier and an increase of the precursor density for the dielectric breakdown. Further, an increase of hopping conductance through localized states is discussed. At energies larger than 150 V the resistance breaks down rapidly and the tunneling magnetoresistance vanishes completely. This results from the enhanced intermixing and sputtering of the barrier and electrode material. The results are also supported by investigations of the magnetic and the noise properties of the junctions and the Cu-${\mathrm{K}}_{\ensuremath{\alpha}}$-reflectivity of ${\mathrm{AlO}}_{x}$ multilayers.