Bombardment Dose Research Articles

Direct diffusion bonding of 1060Al processed by surface activation with various doses of Ar ion bombardment

In this work, the microstructure and properties of the 1060Al surface after bombardment with different doses of Ar ion and the evolution rule of the quality of the subsequent solid-state diffusion bonded joints have been investigated in detail. The results showed that the oxide layer could be removed completely at an appropriate ion bombardment dose (2 × 1018ion/cm, while kept the same energy of 1 keV), the roughness of the surface was also reduced, crystal defects such as dislocation loops formed near the surface, all of the above factors were beneficial for diffusion bonding. Well-bonded joints with a bonding ratio of ∼97.7% and a shear strength of ∼45.9 MPa could be obtained even at lower process parameters (450 °C/90 min, 5 MPa). When the bombardment dose was too low, the residual oxide film and the rough surface were not conducive to atomic diffusion at the interface, resulting in the unbonded defects in the joint. While the irradiated expansion of the 1060Al surface occurred when the bombardment dose was too high, and the bulges would crack under pressure. In both cases, it could not obtain a well-bonded interface, the joints showed a lower shear strength.

Effects of He-ion bombardment on the ferroelectric and dielectric properties of BaHf0.17Ti0.83O3 films

Focused helium ion bombardment provides an effective means to modify the properties of ferroelectric materials. This work systematically investigates the effect of helium ion bombardment on the structural, ferroelectric, and dielectric properties of relaxor BaHf0.17Ti0.83O3 thin films at different bombardment doses in the range of 1 × 1012 to 7 × 1015 ions/cm2. The films show more defects and slightly expanded out-of-plane lattice parameters with an increase in dose. Despite helium ion bombardment introducing more defects and structural disorder in the system, the bombardment-induced dipole polarization leads to enhanced ferroelectricity. Our findings highlight energetic helium ion bombardment as an effective way to enhance the ferroelectricity of relaxor materials.

Defect-mediated sputtering process of boron nitride during high incident angle low-energy ion bombardment

Further development of hexagonal boron nitride (hBN) towards electronic devices requires the application of precise analytical techniques. High incident angle (¿ 65°) secondary ion mass spectrometry has been recently developed, and allows to reach atomic depth. However, the procedure has been optimized experimentally, and thus computer simulations are needed to validate and comprehend the experiment. It is revealed that a sample without any defects cannot be sputtered in such conditions — all ions are reflected from the surface. Only defects, particularly vacancies, can act as erosion centers. After prolong bombardment (dose in the range of 1017 ions cm-2), the number of defects and their sizes are sufficiently large that rapid removal of a top-most hBN layer can be observed. Computer simulations and additional experiments reveal that the sputtering process is defect-mediated and anisotropic — significantly more prominent along the incident direction.

Experimental and theoretical study of the effect of bombardment with Ar+ ions on the spectrum of valence electrons of a Si (111) single crystal

The paper studies the effect of disordering of the surface layers on the electronic and optical properties of single-crystal silicon.An analysis of the photoelectron spectra shows that with complete amorphization of the surface density, the condition of Si valence electrons of changes significantly. In particular, the positions of the main maximum of the electrons of the valence band of Si (111) shift by ~ 0.4 eV towards higher binding energies and the band gap Eg increases by 0.1-0.15 eV. The energy of a valence electron in amorphized silicon, which at low impurity concentrations, i.e. at low bombardment doses (D <1015 cm–2), the potential Mkk and, therefore, the shift of the maximum of the density of states vary linearly with respect to concentration. At high impurity concentrations (at doses D> 1015 cm–2), corresponding to the transition to amorphous silicon, the concentration dependence of Mkk is very weak. Therefore, upon amorphization, the peak A of the density of states of the silicon valence band under consideration is shifted to the region of lower electron binding energies. The theoretical substantiation of the obtained experimental results is given.

In situ disordering of monoclinic titanium monoxide Ti5O5 studied by transmission electron microscope TEM

The superlattice and domain structures exhibited by ordered titanium monoxide Ti5O5 are disrupted by low energy electron beam irradiation. The effect is attributed to the disordering of the oxygen and titanium sublattices. This disordering is caused by the displacement of both oxygen and titanium atoms by the incident electrons and results in a phase transformation of the monoclinic phase Ti5O5 into cubic B1 titanium monoxide. In order to determine the energies required for the displacement of titanium or oxygen atoms, i.e. threshold displacement energies, a systematic study of the disappearance of superstructure reflections with increasing electron energy and electron bombardment dose has been performed in situ in a transmission electron microscope (TEM). An incident electron energy threshold between 120 and 140 keV has been observed. This threshold can be ascribed to the displacements of titanium atoms with 4 as well as with 5 oxygen atoms as nearest neighbors. The displacement threshold energy of titanium atoms in Ti5O5 corresponding with the observed incident electron threshold energy lies between 6.0 and 7.5 eV. This surprisingly low value can be explained by the presence of either one or two vacant oxygen lattice sites in the nearest neighbors of all titanium atoms.

Enhanced End-Contacts by Helium Ion Bombardment to Improve Graphene-Metal Contacts.

Low contact resistance between graphene and metals is of paramount importance to fabricate high performance graphene-based devices. In this paper, the impact of both defects induced by helium ion (He+) bombardment and annealing on the contact resistance between graphene and various metals (Ag, Pd, and Pt) were systematically explored. It is found that the contact resistances between all metals and graphene are remarkably reduced after annealing, indicating that not only chemically adsorbed metal (Pd) but also physically adsorbed metals (Ag and Pt) readily form end-contacts at intrinsic defect locations in graphene. In order to further improve the contact properties between Ag, Pd, and Pt metals and graphene, a novel method in which self-aligned He+ bombardment to induce exotic defects in graphene and subsequent thermal annealing to form end-contacts was proposed. By using this method, the contact resistance is reduced significantly by 15.1% and 40.1% for Ag/graphene and Pd/graphene contacts with He+ bombardment compared to their counterparts without He+ bombardment. For the Pt/graphene contact, the contact resistance is, however, not reduced as anticipated with He+ bombardment and this might be ascribed to either inappropriate He+ bombardment dose, or inapplicable method of He+ bombardment in reducing contact resistance for Pt/graphene contact. The joint efforts of as-formed end-contacts and excess created defects in graphene are discussed as the cause responsible for the reduction of contact resistance.

Mechanisms of oxidation-reduction processes on metal and oxide surfaces under ion bombardment

Surface oxidation occurs if metals are bombarded with low-energy (1–5 keV) ions of a chemically active gas (oxygen) in vacuum. It is ascertained that ion bombardment leads to the generation of lower, intermediate, and higher oxides. The composition and thickness of an oxidized layer depend on the metal reactivity and the dose and energy of oxygen ions. The mechanism underlying the ion-beam oxidation of metal surfaces is proposed. Surface reduction is observed if higher oxides are bombarded with low-energy (1–5 keV) ions of inert gases (argon and helium) in vacuum. It is revealed that ion bombardment not only generates intermediate and higher oxides but sometimes gives rise to surface metallization. The composition and thickness of the reduced layer are determined by the oxide type, the kind of inert gases, and the dose and energy of bombardment. The mechanism describing the ion-beam reduction of higher metal oxide surfaces is proposed.

High Energy Ion Bombardment of Thin Films: From Platinum on Silicon to Platinum Silicide

The effect of high energy ion bombardment on ultra-thin Pt films deposited on silicon substrates was investigated. The changes caused by the bombardment were studied using a combined characterization approach, consisting of X-Ray Photoelectron Spectroscopy (XPS) and electrochemical measurements. The chemical sensitivity of XPS helped determine locally the nature of the film after bombardment, which transitions to platinum silicide, as demonstrated by a dramatic evolution of the Pt4f and valence band spectra. Cyclic voltammetry provided the average electrochemical response of the entire sample surface (1 cm2) in contact with an acidic solution. This technique is particularly sensitive to the evolution of the platinum undergoing bombardment. Initially showing a typical Pt electrochemical response, the film undergoes an irreversible transformation, leading to the absence of any metallic platinum on the surface after a sufficient bombardment dose, based on the absence of electrocatalytic activity. This study highlights the complementarity of XPS and electrochemical characterization. The platinum silicide fabrication technique described here may also be of interest for electronics applications, since platinum silicide contacts are used in a variety of thin film devices.

Changes in the Electrochemical Behavior of Silicon after Platinum Deposition and Ionic Bombardment

The electrochemical response of thin Pt films on Si was studied at different stages of mixing between Pt and Si, from fully segregated to fully mixed. This phase change was induced by subjecting the films to helium ion bombardment at energies in the range of 30 keV. The formation of a PtxSi phase was confirmed by XPS measurements. As the bombardment dose increases, the voltammogram peaks characteristic of bulk platinum eventually disappear, giving way to the practically featureless voltammogram of electrocatalytically inactive platinum silicide.

Variation of the defect density in a-Si:H and μc-Si:H based solar cells with 2 MeV electron bombardment

Improvement of the performance of solar cells based on amorphous (a-Si:H) and microcrystalline (μc-Si:H) silicon requires understanding of the role of the deep defects – dangling bonds – in the bulk of the intrinsic a-Si:H or μc-Si:H absorber layers. A straightforward way to understand how these defects may affect the performance of the cells is to investigate changes in the device performance upon variation in the defect density.In the present work solar cells with a-Si:H and μc-Si:H absorber layers were exposed to 2MeV electron bombardment. The performance of the cells after various bombardment doses and annealing steps was evaluated in view of the changes in the defect density of intrinsic layers, measured with ESR on nominally identical absorber layers irradiated in parallel with the cells.The defect density was varied over a range of 2 orders of magnitude. In the solar cells a strong degradation of performance is observed upon irradiation with the biggest effect on the short circuit current density JSC for both types of absorber layers. In most cases both VOC and JSC recover after the final annealing step (at 160°C) for both types of cells.

Relationship between GMI and Barkhausen Noise in an Ion-irradiated Amorphous Ribbon

The mechanism for the abrupt increase in the giant magneto impedance (GMI) ratio in an ion-irradiated Co-based amorphous ribbon has been investigated. The GMI ratio is considerably increased in the ion-irradiated samples, and the GMI response shows a strong dependence on the driving frequency. For the Ar-ion-irradiated sample, the Barkhausen noise (BN) signals increases with increasing ion dose. The power spectrum density of the BN increases with increasing ion bombardment dose. The results are interpreted on the basis of radiation damage and domain wall dynamics.

Relationships between the Particle Velocity and Introduction of Drug-Loaded Microparticles into the Skin in a Microparticulate Bombardment System

Recently, it has been suggested that a microparticulate bombardment system would be a very useful tool for the delivery of a variety of powdered drugs as an alternative to parenteral injection via a needle. However the relationship between the particle dynamics and introduction into the skin has not been researched using this system. In the present study, we analyzed the velocity of microparticles bombarded by the Helios(TM) gun system under various conditions using particle image velocimetry (PIV). The particle kinetic energy, which depended on the particle velocity and particle mass, was increased with increasing helium pressure and particle size, decreasing bombardment dose, resulting in the increased percentage introduction and relative bioavailability (F(0-24 h)). The particle velocity had a greater influence than the particle mass. Therefore, in order to be the most effective system for introduction into the skin, it is necessary to use a high helium pressure and microparticles of high density. However, it is also necessary to consider the skin damage after bombardment.

Introduction of poly-L-lactic acid microspheres into the skin using supersonic flow: effects of helium gas pressure, particle size and microparticle dose on the amount introduced into hairless rat skin.

A microparticulate bombardment system loaded with DNA- and RNA-coated gold and tungsten microparticles (diameter 1-3 microm; density about 19 g cm(-3)), the Helios gene gun system (Helios gun system), has been used to deliver a gene into cells by accelerating the microparticles to high velocity using a supersonic flow of helium gas. To investigate whether drug-loaded microspheres, > 20 microm in diameter and about 1.0 g cm(-3) in density, could be delivered in powder form quantitatively into the skin using the Helios gun system equipped with a cartridge container fitted with a rupture membrane, we investigated the effect of the helium gas pressure in accelerating indometacin-loaded poly-L-lactic acid (PLA) microspheres, as well as the particle size and the bombardment dose on delivery into the skin. Introduction of indometacin (i.e. indometacin-loaded PLA microspheres) after bombardment, with 3.0 mg indometacin-loaded PLA microspheres of a particle size of 20-38, 44-53 and 75-100 microm at a helium pressure of 100, 200 and 300 psi, of the abdomen of hairless rats increased in parallel with the helium pressure and it was also affected by the particle size, being highest at a diameter of 75-100 microm. However, introduction of higher amounts of PLA microspheres resulted in more severe skin erythema (skin damage) as monitored by the Draize score. Using lower bombardment doses (0.5 and 1.0 mg), the efficiency of introduction was improved and the skin damage markedly reduced. Moreover, discrete bombardment with a low dose provided a more efficient introduction of indometacin and less skin damage. These results suggest that bombardment injection of drug-loaded microspheres in a powdered form by the Helios gun system appears to be a very useful tool for the quantitative delivery of a variety of drugs and an alternative to parenteral injection by needle, especially for delivering water-soluble macromolecules.

Study of corrosion protection of different stainless steels by nanocrystalline plasma electrolysis

The effect of nitrogen and carbon bombardment on the corrosion behavior of three different stainless steels (AISI 304, AISI 316L and AISI 430) is discussed in this work. Nitrogen and Carbon was entered into the lattice in order to generate a rich region near the surface by a relatively new method called plasma electrolysis. Different ion bombardment doses under different applied voltages and thus different electrical fields (230, 245, 260 volts) at 330 mS/Cm of electrical conductivity of specific electrolyte have been tested to optimize the ion bombardment doses for each steel. The corrosion measurements were carried out in sodium chloride solution by using potentiodynamic scanning (PDS) and electrochemical impedance spectroscopy (EIS). The experimental results showed that the effect of N and C ion bombardment mainly depends on the microstructure and/or composition of the stainless steels. Less compact structures and/or less amount of alloying elements (as occurs with the body centered cubic, ferritic AISI 430) achieve bigger changes with this modification, whereas on stainless steels with a larger amount of alloying elements and / or more compact structures (like the face centered cubic, austenitic AISI 316L) ion bombardment slightly modifies the corrosion behavior.

Effect of ion bombardment and annealing on the electrical properties of hydrogenated amorphous silicon metal–semiconductor–metal structures

The electrical properties of hydrogenated amorphous silicon (a-Si:H) metal–semiconductor–metal (MSM) devices are investigated as a function of Si bombardment dose prior to and after annealing. We observe that conduction in unbombarded devices is surface-barrier controlled whereas it is bulk controlled in bombarded devices. The resistance decreases with bombardment dose in a manner consistent with increased hopping conductivity in highly damaged structures. A relative permittivity of between 8 and 12, depending on dose, was calculated from experimental Poole–Frenkel plots for bombarded devices. These values compare closely with the theoretical relative permittivity for amorphous silicon of 11.7 and confirm that conduction is by Poole–Frenkel mechanism. For bulk-controlled conduction, we observe an increase in the zero-field Coulombic trap barrier height with decreasing dose, ranging from 0.53 for a Si dose of 5×1013cm−2 to 0.89 for a dose of 2×1012cm−2. We attribute this to a decrease in the concentration of charged defects with decreasing dose and find that the change in concentration of charged centers needs to be about 4×1019cm−3 to account for the change of 0.35eV from the lower to the upper dose. Activation energies obtained from Arrhenius plots of current density against temperature varied with dose and temperature in a similar way as Coulombic barrier height. We explain these results in terms of the variation in the number of charged defect centers with dose and annealing temperature and a shift in the Fermi level.

Oxide formation during ion bombardment of small silicon structures

The kinetics of high dose oxygen implantation and of surface sputtering in silicon are investigated by atomic force microscopy, transmission electron microscopy, transmission electron holography, and electron energy-loss spectroscopy. The implantation was performed into accurately defined submicrometer areas. The behavior of the erosion rate as a function of the implantation dose proved to be nonmonotonic. After native oxide sputtering, a period dominated by (i) implantation of oxygen and (ii) induced oxide formation with volume increase takes place, causing a maximum surface step around the bombarded area of about 1.1 to 1.3 nm at bombardment doses below 2×1016 O+ cm−2. Subsequently, higher doses cause a sputtering of the surface with a sputter yield of about 0.32 Si atoms/O+. Electron holography revealed the double layer character of the implanted region, and electron energy-loss spectroscopy, especially near the relevant Si-L23 ionization edge, identified these two layers which are (i) amorphous silicon oxide and (ii) amorphized silicon. Electron energy-loss line scans show the oxygen distribution inside the implanted areas with a lateral resolution of about 1–2 nm. It was found that the interface between the oxidized layer and the amorphized silicon sharpens with increasing implantation dose.

Studies on the aqueous corrosion behavior and microstructure of zircaloy4 which has been subjected to high-dose Ar ion bombardment

In order to investigate the ion bombardment effect on the corrosion behavior of zircaloy4, the specimen surfaces were bombarded by Ar ion using an accelerator at an energy of 150 keV with a dose range from 3×10 15 to 1×10 17 ions/cm 2 at liquid nitrogen temperature. Post-bombardment corrosion tests were conducted to rank the corrosion resistance of the resulting specimens by potentiodynamic polarization curve measurements in a 0.5 M H 2SO 4 water solution at room temperature. The vacancy profile induced by Ar ions bombardment was calculated using Monte Carlo simulation program SRIM 96, and measured by means of the slow positron annihilation spectroscopy (SPAS). The surface microstructures were examined using glancing angle X-ray diffraction (GAXRD). The potentiodynamic tests showed that with the bombardment dose increasing, the passive current density, closely related to the surface corrosion resistance, decreased firstly and increased subsequently. The mechanism of the corrosion behavior transformation was due to the amorphous phase formation firstly and the amorphous phase destruction and the polycrystalline structure formation in the bombarded surface subsequently.

Effects of particle size, helium gas pressure and microparticle dose on the plasma concentration of indomethacin after bombardment of indomethacin-loaded poly-L-lactic acid microspheres using a Helios gun system.

We investigated the effects of the particle size of indomethacin-loaded poly-L-lactic acid microspheres (IDM-loaded PLA MS), the helium pressure used to accelerate the particles, and the bombardment dose of PLA MS on the plasma concentration of IDM after bombarding with IDM-loaded PLA MS of different particle size ranges, 20-38, 44-53 and 75-100 microm, the abdomen of hairless rats using the Helios gene gun system (Helios gun system). Using larger particles and a higher helium pressure, produced an increase in the plasma IDM concentration and the area under the plasma concentration-time curve (AUC) and resultant F (relative bioavailability with respect to intracutaneous injection) of IDM increased by an amount depending on the particle size and helium pressure. Although a reduction in the bombardment dose led to a decrease in C(max) and AUC, F increased on decreasing the bombardment dose. In addition, a more efficient F was obtained after bombarding with IDM-loaded PLA MS of 75-100 microm in diameter at each low dose in different sites of the abdomen compared with that after bolus bombardment with a high dose (dose equivalent). These results suggest that the bombardment injection of drug-loaded microspheres by the Helios gun system is a very useful tool for delivering a variety of drugs in powder form into the skin and systemic circulation.

Ion bombardment in surface passivation of GaAs

The electrical properties of SI GaAs substrates after oxygen ion bombardment have been investigated in the temperature range of 150–373K. It was found that the oxygen ion bombardment of poor substrates stabilised their surface electrical properties in the sense of increase of the breakdown voltage. Because of leakage current which increased when the ion dose was increased only ion bombardment for the dose range from 1012 to 5×1012cm−2 may have a practical significance. However, the dose of ion bombardment of 1012cm−2 seems to be optimal. In this case the breakdown voltages were about 50V for a 20μm electrode separation (i.e. 25kV/cm) and leakage sheet current densities were from 3×10−9 to 5×10−8A/mm at the temperature range from 293 to 373K.

X-ray emission study of ion beam mixed Cu/Al films on polyimide

Cu (40 nm)/Al/polyimide/Si was mixed with 80 keV Ar+ and N2+ from 5.0×1015 to 15×1015 ions/cm2. Ultrasoft x-ray emission valence spectra (XES) of Cu, C, N and O excited by electron and photon radiation were used for study of chemical reactions in Cu/Al/PI/Si and PI/Si systems induced by ion beam mixing in dependence of type of ions and dose. It is found that ion beam mixing changes the chemical state of Cu atoms with respect to that of pure metal. These changes depend on the dose of ion beam bombardment and type of ions and are attributed to a formation of CuAl2O4 interfacial layer, which can be responsible for enhanced interfacial adhesion strength. On the other hand, it is shown that the shape of C Kα, N Kα and O Kα XES of ion beam mixed polyimide layer (PI/Si) is modified with ion bombardment. This means that the ion-beam mixing process is able to break the bonding of constituent atoms of irradiated PI layers and can induce the formation of chemically bonded complexes linking atoms in the Cu, Al and PI layers.