Energetic Particle Bombardment Research Articles

Corrosion study of plasma sintered unalloyed iron: The influence of porosity sealing and Ni surface enrichment

Results of corrosion tests on samples produced by powder metallurgy technique are presented. Unalloyed iron samples were compacted at 600 MPa and sintered in a plasma reactor for 1 h at 1150 °C. Sintering was performed in an abnormal glow discharge generated in argon/hydrogen gas mixture using two different electrode configurations. In the first one, the sample acted as the discharge cathode (cathode configuration), being bombarded by energetic ions and fast neutrals. In this geometry, direct heating of the sample is provided by the bombardment of energetic particles. In addition, the bombardment of the sample surface by energetic particles resulted in an improvement of mass transport by volume diffusion and surface diffusion in the sample near to bombarded surface. As a consequence of the shrinkage due to sintering is higher in the outer volume layer of the sample resulting in surface porosity sealing. In the second configuration, the sample was placed on the anode of the discharge (anode configuration), inside a nickel hollow cathode. In this case the heating up of the sample is then obtained by radiation from the cathode. As a consequence of the bombardment of the nickel cathode, Ni atoms sputtered from the cathode were deposited on the sample surface resulting in an enriched Ni layer during the sintering process. Microstructure characterization and chemical composition were performed by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) and X-ray Diffraction (XRD). Conventional electrochemical potentiodynamic tests were carried out in a 0.5 M KNO 3 solution. The surface porosity reduction obtained in cathode configuration resulted in an increment of corrosion resistance. The superficial Ni enrichment obtained by sintering samples using the anode configuration was not sufficiently homogeneous to improve corrosion resistance.

Effect of arc suppression on the physical properties of low temperature dc magnetron sputtered tantalum thin films

Arcing is a common phenomenon in the sputtering process. Arcs and glow discharges emit electrons which may influence the physical properties of films. This article reports the properties of tantalum (Ta) thin films prepared by continuous dc magnetron sputtering in normal and arc-suppression modes. The substrate temperature was varied in the range of 300–673K. The tantalum films were ∼1.8μm thick and have good adherence to 316 stainless steel and single-crystal silicon substrates. The phase of the Ta thin film determines the electrical and tribological properties. The films deposited at 300K using both methods were crystallized in a tetragonal structure (β phase) with a smooth surface (grain size of ∼10nm) and exhibited an electrical resistivity of ∼194μΩcm and a hardness of ∼20GPa. When the substrate temperature was 473K and higher, the arc-suppression mode appears to influence the films to crystallize in the α phase with a grain size of ∼40nm, whereas the normal power mode gave mixed phases β and α beyond 473K, the arc-suppression mode yields larger grain sizes in the Ta thin films and the hardness decreases. These changes in the physical properties in arc-suppression mode are attributed to either the change in plasma characteristics or the energetic particle bombardment onto the substrate, or both.

Comparative study of porosity and pores morphology of unalloyed iron sintered in furnace and plasma reactor

Samples of unalloyed iron were sintered in the presence of an abnormal glow discharge using a confined anode-cathode configuration. The samples were placed on a holder acting as the discharge anode inside an AISI 1020 steel hollow cathode. Heating of the outer cathode was obtained by the bombardment of ions and energetic neutral particles. As a consequence of the confined geometry, the sample was efficiently heated mainly by radiation from the cathode. In order to evaluate the results of the sintering process by plasma, samples of unalloyed iron were also sintered in a resistive furnace using the same thermal cycle. The porosity, dimension and morphology of the pores were characterized by means of four basic parameters: area fraction, mean diameter, shape factor and elongation factor. The results show that the shape factor depends on the pore size, a characteristic that was not observed for elongation factor. For samples sintered in plasma reactor or conventional furnace, no significant difference in the porosity or in the pores morphology was observed.

Nanodiamond growth on diamond by energetic plasma bombardment

The present work studies the growth of nanodiamond under prolonged DC glow discharge plasma bombardment of 1 μm thick polycrystalline CVD diamond. Using Raman spectroscopy, near edge X-ray absorption fine structure (NEXAFS) and secondary ion mass spectroscopy (SIMS) it is shown that nanodiamond formation on diamond starts directly, skipping the nucleation stage required to form the precursor material with the appropriate density and hydrogen content. On the other hand, the amorphous carbon/nanodiamond composite structure is substantial to the nanodiamond nucleation under energetic plasma bombardment and cannot be eliminated by starting with a micro-crystalline diamond substrate. The results give additional insight to the phenomena of nanocrystalline nucleation and growth under energetic particle bombardment relevant to a variety of systems including bias enhanced nucleation of diamond and cBN deposition by ion assisted methods.

Twin target sputtering system with ladder type magnet array for direct Al cathode sputtering on organic light emitting diodes

Twin target sputtering (TTS) system with a configuration of vertically parallel facing Al targets and a substrate holder perpendicular to the Al target plane has been designed to realize a direct Al cathode sputtering on organic light emitting diodes (OLEDs). The TTS system has a linear twin target gun with ladder type magnet array for effective and uniform confinement of high density plasma. It is shown that OLEDs with Al cathode deposited by the TTS show a relatvely lower leakage current density (∼1×10−5mA/cm2) at reverse bias of ‐6V, compared to that (1×10−2∼10−3 mA/cm2 at ‐6V) of OLEDs with Al cathodes grown by conventional DC magnetron sputtering. In addition, it was found that Al cathode films prepared by TTS were amorphous structure with nanocrystallines due to low substrate temperature. This demonstrates that there is no plasma damage caused by the bombardment of energetic particles. This indicates that the TTS system with ladder type magnet array could be useful plasma damage free deposition technique for direct Al cathode sputtering on OLEDs or flexible OLEDs.

Low temperature deposition of nanocrystalline TiO2 films: enhancement of nanocrystal formation by energetic particle bombardment

This paper reports the important role of energetic particle bombardment in achieving low temperature deposition of nanocrystalline TiO2 films by reactive DC magnetron sputtering of Ti targets in a mixture of argon and oxygen. In this work, we studied the effect of particle bombardment in the film deposition process by control of external processing parameters, including total pressure Pt and negative substrate bias Vb. The result shows that the variation of energetic particle bombardment has a significant impact on substrate temperature, crystal structure, surface morphology and refractive index n of deposited TiO2 films and we believe the process of non-equilibrium atomic scale heating caused by energetic particle bombardment is the main reason for the nanocrystal formation at low temperature (below 75 °C).

Microstructural differences in thin film ZnGa2O4:Mn phosphor produced by differences in sputtering gas pressure

The authors report on the microstructural characteristics of sputter-deposited thin film ZnGa2O4:Mn phosphors, with an emphasis on the role of energetic particle bombardment. The thin film ZnGa2O4:Mn phosphors were deposited by radio frequency planar magnetron sputtering of a 2mol% Mn-doped ZnGa2O4 target in an Ar–O2 gas mixture at gas pressures ranging from 2to20mTorr. The growth rate of the ZnGa2O4:Mn films was decreased from 40to23Å∕min as the gas pressure was raised due to both increased gas-phase scattering as well as reduced target self-bias voltage. Owing to the thermalization of impinging energetic particles and the randomization in their incidence directions when arriving at the substrate, the ZnGa2O4:Mn films produced at an elevated gas pressure exhibited a porous composite microstructure in which larger columns consisted of bundles of smaller columns separated by voided boundaries. Energetic particle bombardment of the growing film surface at a low gas pressure yielded a densely packed zone-T-type microstructure due to porosity annihilation by knock-on processes and bombardment-enhanced adatom mobility. Atomic force microscopy and grazing incidence x-ray reflectivity data revealed that as the gas pressure was decreased from 20to2mTorr, the rms surface roughness of the deposited ZnGa2O4:Mn films was reduced from 4.95to1.23nm and the film density increased from 5.314to5.681g∕cm3, consistent with the postulated effects of energetic particle bombardment upon film microstructure.

A Late Episode of Irradiation in the Early Solar System: Evidence from Extinct36Cl and26Al in Meteorites

Late-formed halogen-rich phases in a refractory inclusion and a chondrule from the Allende meteorite exhibit large S-36 excesses that linearly correlate with the chlorine concentration, providing strong evidence in support of the existence of the short-lived nuclide Cl-36 (mean life of 0.43 Myr) in the early solar system. The inferred Cl-36/Cl-35 ratios at the time when these phases formed are very high (similar to 4 x 10(-6)) and essentially the same for the inclusion and the chondrule and confirm the earlier report of S-36 excess in another meteorite. In addition, the Cl-36 is decoupled from Al-26. The observed and any possible higher levels of Cl-36 cannot be the result of a supernova or AGB stellar source but require a late episode of energetic particle bombardment by the early Sun, in support of the arguments based on the previous discovery of Be-10. It is now clear that a blend of several sources is required to explain the short-lived nuclei when the solar system formed.

Understanding the Kinetics and Dynamics of Radiation‐induced Reaction Pathways in Carbon Monoxide Ice at 10 K

Carbon monoxide is the second most abundant molecule on icy grains in the interstellar medium. It also exists on Pluto, Triton, comets, and possibly in other icy bodies of the outer solar system like Kuiper Belt objects. With the intense radiation fields that permeate virtually all unprotected regions of space, carbon monoxide ices can be processed through energetic particle bombardment (planetary magnetospheric particles, solar wind, Galactic cosmic ray particles, and UV photons). In the present study we have investigated the effects by condensing a 1 � m layer of carbon monoxide ice on a substrate at 10 K and irradiated the sample with energetic (keV) electrons. These simulate the energetic electrons trapped in magnetospheres of planets and reproduce the irradiation effects of typical Galactic cosmic ray particles. A series of new carbon-chain (C3 ,C 6) and carbon oxide species were observed including the linear isomers of C2O, C3O, C4O, C5O, C6/7O, CO2 ,C 3O2 ,C 4O2, and C5O2. A reaction model was proposed that outlines different reaction pathways to each of these products. Using this model, the kinetics of each route of reaction wasquantified,andfromthis,themechanismsanddynamicsofthereactionscanbeunderstood.Thisworkshouldaid in the astronomical detection of new molecular species in solar system ices as well as building up a comprehensive reaction model to describe the chemical inventory of ices on interstellar dust grains. Subject headings: astrochemistry — comets: general — cosmic rays — infrared: ISM — ISM: molecules — methods: laboratory — molecular processes

Direct Al cathode layer sputtering on LiF∕Alq3 using facing target sputtering with a mixture of Ar and Kr

Using facing target sputtering (FTS) with a mixture of Ar and Kr, direct Al cathode sputtering on LiF∕Alq3 layers was accomplished without the need for a protective layer against plasma damage. Organic light emitting diodes (OLEDs) with a directly sputtered Al cathode in a mixture of Ar and Kr showed a much lower leakage current density (∼1×10−5mA∕cm2 at −6V) than those (∼1×10−1mA∕cm2 at −6V) of OLEDs with an Al cathode prepared by FTS or dc sputtering in a pure Ar ambient. This indicates that the bombardment of energetic particles is effectively restricted by mixing a heavy noble gas. Based on the current-voltage curve for the OLED, a possible mechanism is proposed to explain the effect of a heavy noble gas mixture on electrical properties of OLEDs for direct Al cathode sputtering by FTS.

Transparent indium zinc oxide top cathode prepared by plasma damage-free sputtering for top-emitting organic light-emitting diodes

We report on plasma damage-free sputtering of an indium zinc oxide (IZO) top cathode layer for top-emitting organic light-emitting diodes (TOLEDs) by using a box cathode sputtering (BCS) technique. A sheet resistance of 42.6Ω∕cm and average transmittance above 88% in visible range were obtained even in IZO layers deposited by BCS at room temperature. The TOLED with the IZO top cathode layer shows electrical characteristics and lifetime comparable to a TOLED with only thermally evaporated Mg–Ag cathode. In particular, it is shown that the TOLED with the IZO top cathode film shows very low leakage current density of 1×10−5mAcm2 at reverse bias of −6V. This suggests that there is no plasma damage caused by the bombardment of energetic particles during IZO sputtering using the BCS system.

Study of Magnetron Sputter Deposition of Metal Gate Electrodes

AbstractA systematic study of magnetron sputter deposition of metal gate is presented. On-wafer probes were used to measure ion current and floating voltage. Charge monitoring wafers was used to evaluate charging damage. C-V measurements showed that the interface trap density of metal gated MOS capacitors was reduced with thicker dielectric layer thickness and with the insertion of ALD deposited buffer layer. Lower pressure, higher sputtering power, and pulsed DC sputtering were found to cause larger plasma damage to the ultra-thin dielectric layer, most likely due to increased energetic particle bombardment as a result of higher plasma density and higher ion and neutral energies.

Study of metal gate deposition by magnetron sputtering

A systematic study on metal gate deposition by magnetron sputtering is presented. The authors compared the interface trap density (Dit) in metal-oxide-semiconductor capacitors with metal gate deposited by either conventional magnetron sputtering, atomic layer deposition followed by conventional sputter deposition, or a newly developed magnetron sputtering technology. The results indicate that the new sputtering technology can minimize plasma damage to the underlying ultrathin dielectric film and achieve Dit values of less than 1011cm−2eV−1⁠. Experimental data on plasma characterization using ion collectors and Langmuir probe are presented. The effects of metal gate deposition methods, dielectric film thickness, and sputtering parameters such as sputtering power, pressure, and pulsed dc sputtering are discussed. It is found that pulsed dc sputtering generates higher Dit values. In the new sputtering process, the flux and the energy of the ions arriving at the substrate surface are several times lower, and the floating voltage fluctuations on the substrate surface are about one order of magnitude lower, effectively preventing potential plasma damage to the underlying dielectric films by minimizing energetic particle bombardment and charging impact.

Theoretical Investigation of Structure and Stability of Reidinger Defects in Barium Magnesium Aluminate

An atomistic simulation method has been used to study the equilibrated geometry, defect structure, and phase mixing of barium magnesium aluminate (BAM) and related compounds. The calculated lattice energies are used to study the stability of defect structures in the β-alumina lattice, particularly in the presence of excess alumina in the starting materials. It is shown that excess alumina in the starting compounds could lead to the formation of Reidinger defects in BAM. The calculated structural modification of the lattice due to a Reidinger defect is in excellent agreement with the experimental results. These defects are responsible for generation of and F-type color centers by (vacuum) ultraviolet radiation and bombardment of energetic particles from the discharge. BAM could be made resistant to the formation of color centers by adhering to a strictly stoichiometric formulation of this phosphor.

Collision-Induced Dissociation of Water into Ions

A modification of the central force model (CFM) that describes the dissociation of water molecules into OH- and H+ ions is proposed for molecular dynamics simulations of energetic particle bombardment of water ice. The model keeps all the properties of the CFM but permits charge exchange between oxygen and hydrogen atoms when the water molecule starts to dissociate after collision with an energetic projectile. The reaction products, therefore, have the correct integer charges, -1 and +1 for hydroxyl and a proton. The threshold for the ionic dissociation is corrected to be at the right value, 17.2 eV, in a vacuum. Using the proposed model, total cross-sections for ionic dissociation as functions of the projectile energy are estimated for Ar and C projectiles colliding with water molecules in a vacuum and water ice. Carbon projectiles are demonstrated to produce more dissociated ions at energies lower than 300 eV. Argon projectiles are more effective in breaking the molecules at higher energies.

Molecular dynamics simulation of sputtering from a cylindrical track: EAM versus pair potentials

Molecular dynamics simulations implementing the thermal spike model for sputtering by energetic particle bombardment are performed for a gold target represented with a many-body embedded atom method (EAM) potential. A linear dependence of sputtering yield on the effective energy deposition is observed over a broad range of sufficiently high excitation energies, suggesting that the conclusions of earlier simulations performed with pair potentials have a general character and are not sensitive to the choice of interatomic potential. At the same time, significant differences in cluster ejection are observed between the simulations performed with EAM and pair potentials. Clusters constitute a much larger fraction of the total yield in the EAM simulations, which is related to the environmental dependence of the interatomic interaction in metals that is correctly reproduced by EAM potential. An apparent disagreement between the analytical thermal spike model and its implementation in MD simulations cannot be attributed to the choice of interatomic potential but reflects a difference in the ejection mechanisms. Thermally activated evaporation from the surface is assumed in the analytical thermal spike model, whereas prompt ejection from a relatively deep part of the excited region and fast non-diffusive cooling of the spike region takes place in MD simulations.

High temperature erosion of beryllium

The erosion behavior of solid beryllium surfaces exposed to plasma bombardment at high temperature is investigated. The experimentally measured erosion rate of surfaces exposed to energetic particle bombardment at elevated temperature exceeds that predicted by a summation of the physical sputtering rate and the thermodynamic sublimation rate. A model based on the creation of surface adatoms, due to energetic projectile bombardment of surfaces, and their subsequent sublimation is used to explain the enhanced erosion. Molecular dynamics (MD) simulations of beryllium confirm that the experimentally measured evaporation energy (∼2eV) is consistent with the binding energy of adatoms. Of critical importance in this model is the creation rate of adatoms during the surface bombardment. The experimental dependence of the increased erosion on the incident particle flux, particle species and incident particle energy is presented and discussed in relation to the adatom model.

Plasma damage-free deposition of Al cathode on organic light-emitting devices by using mirror shape target sputtering

We report on the fabrication of plasma damage-free organic light-emitting devices (OLEDs) by using a mirror shape target sputtering (MSTS) technique. It is shown that OLEDs with Al cathode deposited by the MSTS show much lower leakage current (1×10−5mA∕cm2) at reverse bias of −6V, compared to that (1×10−1–∼10−2mA∕cm2 at −6V) of OLEDs with Al cathodes grown by conventional dc magnetron sputtering. This indicates that there is no plasma damage, which is caused by the bombardment of energetic particles. This suggests that MSTS could be a useful plasma damage-free and low-temperature deposition technique for both top- and bottom-emitting OLEDs and flexible displays.

Influence of Hydrogen Plasma Treatment and Post-Annealing on Defects in 4H-SiC

In this work, we have investigated the influence of hydrogen plasma treatment on defects in 4H-SiC. Hydrogen was incorporated in 4H-SiC single crystals by plasma treatment, and its effects were characterized by current–voltage measurements and deep-level transient spectroscopy. The reverse leakage current level reduction and the Schottky barrier height increase after hydrogen plasma treatment could be explained by Fermi level (FL) pinning and interface states passivation. Plasma-induced defects were formed by the bombardment of energetic particles on the crystal lattice, but they were annealed out at low annealing temperatures of 400–500°C. Considering the annealing temperature, it can be concluded that these defect levels are related to the carbon vacancy defects. It was also revealed by I–V measurement that the hydrogen passivation of defects was maintained up to 500°C.

TiN thin films deposited by ion beam sputtering: effects of energetic particles bombardment

The low energy broad argon ion beam (1.35–2.0) keV was used for sputtering of a Ti target in an atmosphere of nitrogen gas to form TiN films. During deposition the growing thin film was under argon ion irradiation from the beam periphery. The influence of the ion beam energy ( E b) and average energy delivered by assisting ions to condensing film atoms ( E n) on TiN film properties was investigated. The titanium nitride thin films were deposited at a low working pressure of 1×10 −4 mbar and at ambient substrate temperature. XRD analysis revealed the formation of a δ-TiN phase with preferred (220) orientation for the stoichiometric composition of TiN films (RBS). The increase of both the intensity of the (220) peak and TiN film crystallite dimension with increasing the energy of Ti target bombarding Ar + ions ( E b) was observed. By increasing the average ion energy per deposited metal atom ( E n) the (220) peak intensity and crystallite dimension decrease and a complete loss of (220) orientation at E n close to 162 eV/at was found. In the range of E n considered, the TiN films grain size decreases leading to the nano-structured surface as revealed by the STM analysis. The incident angle and energy of the assisted bombarding strongly influence the film-preferred orientation and sub-microstructure.