Increasing Ion Dose Research Articles

Hydrogen implantation in lanthanum thin films for ambient pressure hydride formation

Near room temperature superconductivity of metal superhydrides has been shown both theoretically and experimentally at high pressures (>100 GPa). Taking advantage of room temperature superconductivity for engineering applications requires decreasing the pressure of formation while retaining the superconducting hydride phase. We implanted lanthanum thin films with various doses of hydrogen ions at ambient pressure in order to form a lanthanum hydride phase. We found evidence for granular superconductivity below 5 K consistent with the phase coexistence of lanthanum hydride and lanthanum. As the H+ dose increased, TC decreased from 4.6 K to 3.2 K with broader superconducting transitions. Transmission electron microscopy showed increased substrate damage with increased ion dose and confirmed the granular structure of the films. Although a superhydride phase requires a higher H+ dose than what was attained in this work, we have demonstrated that ion implantation at ambient pressure is a feasible technique for superconducting lanthanum hydride formation.

Spectromicroscopic study of the transformation with low energy ions of a hematite thin film into a magnetite/hematite epitaxial bilayer

The search of new properties in novel oxide heterostructures requires the exploration of new fabrication methods and the study, at the microscopic level, of the processes involved during the synthesis. We present a synchrotron-based spectromicroscopic investigation of a magnetite/hematite bilayer on Pt(111) grown in a two-step process by thermal evaporation and Low Energy Ion Bombardment (LEIB). The characterization includes the study of structural, electronic, chemical, and magnetic properties using X-ray Absorption Spectroscopy (XAS), Low Energy Electron Microscopy (LEEM), Photoemission Electron Microscopy (PEEM), or X-ray Magnetic Circular Dichroism (XMCD). The aim is to obtain microscopic information of the thin film before, during, and after the ion bombardment. Ion bombardment gradually transforms the topmost layers of the hematite thin film into a defective sub-oxide, where magnetite nuclei grow and coalesce with increasing ion doses. Two rotational domains of magnetite coexist, which are typically a few tens of nanometres large and do not grow significantly with temperature annealings. The incoherent growth of the magnetite nuclei favours the formation of stable twin boundaries (TBs) and antiphase boundaries (APBs). Dichroic spectra show the characteristics of the ferrimagnetic (FiM) order of magnetite, and the spatial distribution of magnetic domains shows no apparent correlation with the structural image, displaying smooth domains separated by diffuse frontiers. These findings illustrate the importance of a spectromicroscopic characterization of novel oxide heterostructures for potential future applications.

Tailoring surface electronic properties of GO-TiO2 hybrid nanostructures through interface modifications

The tailoring of electronic properties in carbon-based hybrid functional materials is essential for improving their overall physicochemical behavior. In this work, graphene oxide (GO)-titanium dioxide (TiO2) hybrid nanostructures are irradiated with 120 MeV Ag9+ swift heavy ions (SHI) for tailoring its surface electronic properties through defect-mediated interface modifications. The microscopic and spectroscopic characterizations indicate a gradual reduction of GO into reduced graphene oxide (rGO) with increasing ion dose. The work function (WF) measurement of GO-TiO2 by scanning Kelvin probe microscopy (SKPM) exhibits systematic variation with the ion fluence and agrees well with the variation in the Fermi energy of GO obtained from the Raman spectroscopy. Moreover, the semiconducting behavior of GO can be effectively tuned by TiO2-controlled Fermi level modulation in GO-TiO2 hybrid nanostructures with ion fluence. The Monte Carlo-based simulations, stopping range of ions in matter (SRIM) and transport of ions in matter (TRIM) codes, reveal that the mutual interplay of defects created in the nanostructures, substrate, and their interfacial regions are responsible for the systematic modulation of the WF in the GO-TiO2.

Structural, surface and optical investigations of Cu+ implanted NiO film prepared by reactive sputtering

Nickel oxide (NiO) films were deposited on silicon substrate using a DC magnetron sputtering system. The deposited films were annealed at 400 °C for 2 h and then irradiated by 500 keV copper ions (Cu+) in the dose range of 1 × 1011 to 1 × 1014 ions-cm−2 using Pelletron Accelerator. X-ray diffraction study revealed NiO and Ni phases in the films corresponding to (111) and (200) planes. The lattice parameter was increased with the increase of ion dose to 1 × 1012 ions-cm−2 and then decreased at the higher doses. Ion irradiation at 1 × 1011 ions-cm−2 improved the crystallinity of the film while at the higher doses, the crystallinity was decreased. The surface morphology of the films showed a decrease in the compactness of the granular structure with increasing the ion dose. Fourier Transform Infrared spectroscopy showed Cu–O and Ni–O stretching vibration peaks in the irradiated films. X-ray photoelectron spectroscopy (XPS) results revealed a decrease in NiO and increase in the Ni+3Ni+2 ratio with an increase of the ion dose to 1 × 1012 ions-cm−2, demonstrating an increase in the Ni vacancies in the film at lower doses. The depth-resolved XPS analysis displayed a change in the Ni and O atomic percentages in the film with the increase of the etching time from 50 to 250 s and validated the existence of metallic Ni in the NiO film. The photoluminescence (PL) spectra analysis showed a decreasing trend in the band gap of the NiO film irradiated up to 1 × 1012 ions-cm−2, then an increasing trend at the higher doses.

Influence of Proton Ion Irradiation on the Linear–Nonlinear Optoelectronic Properties of Sb40Se20S40 Thin Films at Different Fluences for Photonic Devices

This study investigates the effects of 30 keV proton ion irradiation on the structural, morphological, and linear–nonlinear optoelectronic properties of Sb40Se20S40 thin films. The retention of an amorphous nature and vibrational bonding rearrangements caused by ion irradiation demonstrate structural tailoring. The cumulative decrease in roughness with an increase in ion dose decreases the surface energy and optical absorption loss. With the blue shifting of the absorption edges, proton irradiation increased the optical transmittance and reflectance. The variation of fluence changes the optical bandgap and Urbach energy, which are induced by local structural changes caused by defects and disorder. The refractive index decreased considerably, which supports the Moss rule. Proton irradiation reduced the interband transition and average band energy gap of the system. However, ion irradiation increased optical losses while decreasing optical conductivity and dielectric characteristics. The third-order nonlinear susceptibility and nonlinear refractive index decreased significantly as the fluence increased. Such materials with optical tuning capabilities via ion fluence are essential for cutting-edge photonic and optoelectronic applications.

Electron transport tuning of graphene by helium ion irradiation

This article reviews charge carrier transport phenomena in single-layer graphene, in which crystalline defects are generated by helium-ion-beam irradiation using a helium-ion microscope. Crystalline defects work as electron scatterers, and the conductivity drastically decays as ion dose increases. Moreover, real-time conductivity monitoring during ion beam scans over the graphene surface is demonstrated. In cryogenic measurements under magnetic fields, defective graphene exhibits negative magnetoresistance, suggesting that strong localization occurred in this two-dimensional electron system, which survived even at room temperature. The localized state contributes to inducing a transport gap around the Dirac point, where the density of states is at its minimum, and it enables field-effect control of the carrier transport by tuning the carrier density. The fabrication and operation of field-effect transistors with defective graphene channels are demonstrated.

Effect of ion implantation on mechanical strength of silicon wafers

We have investigated the effects of the secondary defects caused by ion implantation on wafer strength. The change in wafer strength with the ion dose has been examined after implanting phosphorus or (BF2)+ ions into wafers with and without heat treatment. Ion implantation defects have been observed using transmission electron microscopy after ion implantation with and without subsequent annealing. The three-point bending tests carried out with the ion implanted samples show that the upper yield stress, which represents wafer strength, gradually decreases with the increasing dose in the case of phosphorus ions and rapidly decreases in the case of (BF2)+ ions due to the formation of secondary defects. In addition, the strength of the wafers with a low oxygen concentration is lower than that of the wafers with a high oxygen concentration. However, the rate of decrease in wafer strength with increasing ion dose is not affected by the oxygen concentration; it only depended on the implanted element.

Helium bubble formation and evolution in NiMo-Y2O3 alloy under He ion irradiation

We report helium ion irradiation experiments for a new type of dispersion-strengthened NiMo-Y2O3 alloy with three different irradiation doses and varying irradiation dose rates at 750 °C to evaluate its helium-induced damage behavior. Transmission electron microscopy was used to reveal the evolution of helium bubbles after irradiation. The experimental results show that with increasing ion dose, the number density of helium bubbles increases continuously. However, the mean size of helium bubbles first increases and then decreases, mainly due to the varied ion dose rates. The volume fractions of helium bubbles in the three investigated samples after irradiation are 0.15%, 0.32%, and 0.27%, which are lower than that of the Hastelloy N alloy (0.58%) after similar irradiation conditions. This indicates that the NiMo-Y2O3 alloy exhibits better helium-induced-swelling resistance than the Hastelloy N alloy, highlighting its potential applicability to MSRs, from the perspective of irradiation performance.

Quantitative hydrogen state analysis in the leached layer of soda-lime-silica glass by combination of nuclear reaction analysis and C60-X-ray photoelectron spectroscopy

The effects of acid treatment on the surface layer of soda-lime-silica glasses were investigated by nuclear reaction analysis (NRA) and C60-X-ray photoelectron spectroscopy (XPS) in a depth-resolved manner. As the time of treatment with HCl increased, the amount of H increased and was distributed in a region at a depth of almost 150 nm. In the near-surface region, however, the damage due to 15N2+ beam irradiation for conducting the NRA was found to be substantial as observed by the fast decay of signal intensity with increasing ion dose. The depletion of sodium, magnesium, and calcium in the surface layer was examined by C60-XPS. Sodium was depleted at a depth of 150 nm by the acid treatment, but the depletion of magnesium and calcium occurred at a depth within approximately 30 nm. Assuming the ion exchange reaction between the alkaline and alkaline earth elements with H3O+, the Si-OH concentration profile was evaluated from the depletion profiles of sodium, magnesium, and calcium. From the difference between the Si-OH profile and H distribution obtained by NRA, the H2O/Si-OH ratio in the leached layer was estimated at 1.3.

Optical band gap tailoring of muscovite mica via monolayer modification by ultra-low energy ion beam sputtering

In this paper, we report the band gap tailoring of naturally available muscovite mica by ultra-low energy (300 eV) Ar+ ion sputtering at normal ion incidence. The muscovite mica is an insulating material (wide band gap ~ 6 eV) having various potential applications from biological substrate deposition to electronic device fabrication. The first monolayer of mica is modified by ultra-low energy ion beam, which leads to the reduction of optical band gap. The ion dose is varied to study the optical band gap information. It is observed that the band gap decreases significantly with increasing ion doses. By varying ion doses, the indirect band gap could be tailored from 2 eV to 1.1 eV, which indicates the semiconducting nature of mica surface. The optical responses of pristine and modified mica are studied by UV–Visible Spectrophotometry and the band gap is calculated from Tauc's plot. The band gap narrowing is supported by the band gap estimation of modified mica from Conductive Atomic Force Microscopy (C-AFM) analysis. The X-ray photoelectron spectroscopy (XPS) study shows that ion bombardment sputters most of the K atoms and other elements in mica along with Carbon adsorption, which leads to change the density of states of mica, resulting in the tailoring of band gap. The surface morphology study of ion modified mica surfaces, investigated by Atomic Force Microscopy (AFM), shows the formation of random rough surface, which transform to irregular pillar like structure at longer time of ion irradiation.

Tuning surface wettability of molybdenum oxide nanorod mesh by low energy ion beam irradiation

In this work, we have studied low energy argon ion-induced modification of surface wetting property of molybdenum dioxide nanorod mesh. The nanorods were deposited on a conductive silicon substrate using a spin coating process. The coated thin films were irradiated at two different fluences of 5 × 1016 and 1 × 1017 ions cm−2, respectively. With increasing ion doses, the nanorods tend to bend slightly and a kinky structure is observed in a cross-geometry. While the surface of the as-deposited sample is hydrophilic, the irradiated surface alters into hydrophobic. We have analyzed the morphological and structural properties of the surface in detail to realize the initial and altered wetting properties. Furthermore, the dynamical variations in the contact angle on the molybdenum dioxide surfaces are further investigated to understand the interactions between the water droplet, the sample surface, and the atmosphere. We foresee that such altered surfaces can be helpful to fabricate corrosion-resistant devices.

Damage profile evolution model based on the Boltzmann transport equation for silicon micromachining with the focused helium ion beam

In this work, a damage profile evolution model based on the Boltzmann transport equation was developed for silicon micromachining using the focused helium ion beam. The energy grouping method, the spherical harmonic function expansion method, and the discrete ordinate method were used to solve the model numerically to obtain the implanted ion distribution and the amorphous damage profile. The influence of the ion beam energy and the ion dose on the evolution of the amorphous damage profile and the helium ion distribution in the silicon substrate were investigated. The implantation depth of the ions was positively correlated with the beam energy, and the influence of the ion dose on the implantation depth of the ions was very slight. The amorphous damage profiles predicted by the model were in good agreement with the experimental transmission electron microscope images. The results showed that the amorphous damage profile evolved into an approximately cylindrical shape for low beam energy (<10 keV), and an approximate “vase” shape for high beam energy (>10 keV). For the specified beam energy, the maximum amorphous width increased linearly and the amorphous depth first increased rapidly and then slowly increased with the increasing ion dose, and there was a limit on the amorphous depth. The computational efficiency of the model was not limited by the number of particles, which made up for a common shortcoming of the Monte Carlo and molecular dynamics methods.

A macro-scale ruck and tuck mechanism for deformation in ion-irradiated polycrystalline graphite

A vein structure, which becomes more pronounced with increasing ion dose, was found on the surface of polycrystalline HOPG (highly oriented pyrolytic graphite) implanted by ex situ C+ (up to 1.8 × 1017 ions/cm2), and in situ Ar+ in a transmission electron microscope (TEM). These veins are found to be independent of the crystallographic orientations and are associated with the formation of pores. Underneath the veins, a triangular-shaped core was formed with the graphite platelet inside the core displaced up towards the surface. A macro-scale ‘ruck&tuck’ geometry was thus generated at these triangle structure boundaries. Progressive movement of dislocations along basal planes during irradiation was observed, and a mechanistic model was proposed on this basis to explain the vein formation. A small increase of c-spacing was observed with irradiation but it is believed that macro-scale vein formation plays a more vital role in the dimensional and property changes in polycrystalline graphite, especially when a stress gradient is present. The model proposed also explains the change of thermal expansion in HOPG with irradiation. Together with Heggie’s ‘ruck&tuck’ and Barsoum’s ‘ripplocations’ models, the present model is considered to have provided an additional experimentally proven mechanism responsible for irradiation behaviour in graphite materials.

Nanoindentation Study on the Creep Characteristics and Hardness of Ion-Irradiated Alloys.

The Hastelloy N alloy, Alloy 800H and 316H stainless steel were irradiated by Xe20+ ion irradiation with energy of 4 MeV at room temperature (peak damage ranging from 0.5 to 10 dpa). The micromechanical properties, hardness and creep plasticity, of these three investigated alloys were characterized before and after irradiation using nanoindentation. The results show that the hardness increases, and creep plasticity degrades with increasing ion dose in all the samples. In comparison, Hastelloy N has good irradiation damage resistance, while that of the 800H and 316H alloys is slightly worse. Additionally, the approximate positive relationship between irradiation hardening and creep plasticity degradation means that the property of creep plasticity of irradiated materials can be reflected from the nanohardness measurement for the heavy ion irradiation cases.

Controlled Manipulation and Multiscale Modeling of Suspended Silicon Nanostructures under Site-Specific Ion Irradiation.

In this work, controlled bidirectional deformation of suspended nanostructures by site-specific ion irradiation is presented. Multiscale modeling of the bidirectional deformation of nanostructures by site-specific ion irradiation is presented, incorporating molecular dynamics (MD) simulations together with finite element analysis, to substantiate the bending mechanism. Strain engineering of the free-standing nanostructure is employed for controlled deformation through site-specific kiloelectronvolt ion irradiation experimentally using a focused ion beam. We report the detailed bending mechanism of suspended silicon (Si) nanostructures through ion-induced irradiations. MD simulations are presented to understand the ion-solid interactions, defects formation in the silicon nanowire. The atomic-scale simulations reveal that the ion irradiation-induced bidirectional bending occurs through the development of localized tensile-compressive stresses in the lattice due to defect formation associated with atomic displacements. With an increasing ion dose, the evolution of localized tensile to compressive stress is observed, developing the alternate bending directions calculated through finite element analysis. The findings of multiscale modeling are in excellent agreement with the bidirectional nature of bending observed through the experiments. The developed in situ approach for bidirectional controlled manipulation of nanostructures in this work can be used for nanofabrication of numerous novel three-dimensional configurations and can provide a route toward functional nanostructures and devices.

Local structure of Ni80X20 (X: Cr, Mn, Pd) solid-solution alloys and its response to ion irradiation

The local structure of Ni80X20 (X: Cr, Mn, Pd) solid-solution alloys was investigated with x-ray absorption and total scattering x-ray diffraction methods. Atomic pair distribution function (PDF) analysis indicated that the local lattice distortion is strongly relevant to the atomic size mismatch, and the local lattice distortion in Ni80Pd20 alloy is obviously larger than that in other solid-solution alloys. The bond length of different atomic pairs was derived from the fitting of extended x-ray absorption fine structure spectra. Quantitative analysis of the local bonding environment in Ni80Cr20 during Ni ion irradiation suggested that Cr atoms tend to form clusters in Ni80Cr20 with the increase of ion dose.

Enhancement of hydroxyapatite dissolution through structure modification by Krypton ion irradiation

Hydroxyapatite (HA) synthesized by a wet chemical route was subjected to heavy ion irradiation, using 4 MeV Krypton ion (Kr17+) with ion fluence ranging from 1 × 1013 to 1 × 1015 ions/cm2. Glancing incidence X-ray diffraction (GIXRD) results confirmed the phase purity of irradiated HA with a moderate contraction in lattice parameters, and further indicated the irradiation-induced structural disorder, evidenced by broadening of the diffraction peaks. High-resolution transmission electron microscopy (HRTEM) observations indicated that the applied Kr irradiation induced significant damage in the hydroxyapatite lattice. Specifically, cavities were observed with their diameter and density varying with the irradiation fluences, while a radiation-induced crystalline-to-amorphous transition with increasing ion dose was identified. Raman and X-ray photoelectron spectroscopy (XPS) analysis further indicated the presence of irradiation-induced defects. Ion release from pristine and irradiated materials following immersion in Tris (pH 7.4, 37 ℃) buffer showed that dissolution in vitro was enhanced by irradiation, reaching a peak at 0.1dpa. We examined the effects of irradiation on the early stages of the mouse osteoblast-like cells (MC3T3-E) response. A cell counting kit-8 assay (CCK-8 test) was carried out to investigate the cytotoxicity of samples, and viable cells can be observed on the irradiated materials.

Enhanced diffusion and bound exciton interactions of high density implanted bismuth donors in silicon

This study reports the effect of an increasing ion dose on both the electrical activation yield and the characteristic properties of implanted bismuth donors in silicon. A strong dependence of implant fluence is observed on both the yield of bismuth donors and the measured impurity diffusion. This is such that higher ion concentrations result in both a decrease in activation and an enhancement in donor migration through interactions with mobile silicon lattice vacancies and interstitials. Furthermore, the effect of implant fluence on the properties of the Si:Bi donor bound exciton, D0X, is also explored using photoluminescence (PL) measurements. In the highest density sample, centers corresponding to the PL of bismuth D0Xs within both the high density region and the lower concentration diffused tail of the implanted donor profile are identifiable.

Effect of temperature on GaSb nanocell lattice fabrication by void formation and development utilizing a focused ion beam

The effect of sample temperature on GaSb nanocell fabrication using a focused ion beam was investigated. Two-dimensional nanocell lattices with a cell interval of 100 nm were fabricated on GaSb at 135 K and 293 K. It was shown that the lattice develops slowly at 135 K with increasing ion dose, and that it does so quickly at 293 K, being disturbed by newly created secondary voids. These results were discussed using the migration parameters of point defects deduced from the recovery data of electron-irradiated GaSb by [Thommen, Phys. Rev. 161, 769 (1967)].

The effect of N+ ion-implantation on the corrosion resistance of HiPIMS-TiN coatings sealed by ALD-layers

Plasma immersion ion implantation (PIII) was studied as a pretreatment method for improving the surface activity of TiN coatings deposited by high power impulse magnetron sputtering (HiPIMS) before being sealed with an ALD (Atomic layer deposition)-Al2O3 hybrid coating. The effect of different implantation energy and dose of nitrogen plasma on the microstructure and surface morphology of TiN coatings were investigated, and the surface morphology and fracture cross-section images of TiN/Al2O3 hybrid coatings with and without PIII pretreatment were compared. The corrosion protection properties were explored with linear sweep voltammetry in 3.5% NaCl solution at the room temperature. The results indicated that the N+ pre-ion-implantation had a significant influence on the microstructure and surface morphology of TiN coatings. With the increase of ion implantation energy and dose, TiN coatings gradually alter from the preferred orientation (200) to a mixture of (200) and (111), accompanied by the decrease of grain size on the surface. Moreover, the PIII pretreatment of the TiN coatings could significantly shorten the incubation time of the nucleation of ALD films, leading to a denser but thinner (at the same deposition cycles) layer of Al2O3, which plays a positive role in corrosion resistance. The coverage of ALD-Al2O3 films was improved with the increase of the nitrogen ion implantation energy and dose, resulting in better corrosion protection.