Ion Beam Parameters Research Articles

Ion incidence angle-dependent pattern formation on AZ® 4562 photoresist by reactive ion beam etching

Reactive ion beam etching is a key technology in the field of ultra-precise surface engineering. In this process nanopatterns can emerge and alter the functional properties of the surfaces. Therefore, it is necessary to understand which reactive ion beam parameters influence the emergence of these nanopatterns. In this study the influence of reactive ion beam etching on the commercially available photoresist AZ® 4562 is investigated. Atomic force microscopy and scanning electron microscopy reveal the formation of nanopatterns (ripples, triangular features, protrusions, facets) depending on a wide range of ion incidence angles (0°–75°) as well as the etch time. The emerged nanopatterns resemble those known from inorganic materials and therefore, lead to the assumption that local redeposition, surface viscous flow and dispersion plays an important role for the pattern formation on polymer surfaces. Major difference from ion beam erosion with inert species is the absence of nanoholes. Spectroscopic ellipsometry shows that the thickness of the modified surface layer depends on the ion incidence angle but not on the fluence in the investigated range. Using X-ray photoelectron spectroscopy, trends of the chemical composition of the surface/near-surface region were detected, which depend on ion incidence angle and etch time.

Anisotropic wettability transition on nanoterraced glass surface by Ar ions

Ion beam sputtering (IBS) can induce nanoripple patterns in a short time on variety of materials for wide range of applications. In this work, we describe the nanoripple as well as terrace pattern formation by IBS on soda-lime glass surfaces and the mechanisms leading to such pattern formations. The role of ion energy, ion fluence, and ion incidence angle on the morphology of the structural features is systematically explored. For a range of ion beam parameter values with energy varying from 600 to 1500 eV and fluence in the range 9.7 × 1017 to 2.0 × 1019 ions/cm2 at fixed incidence angle of 45°, transition of ripples to terraces has been observed. The experimental results are explained on the basis of recently modified KS equation which clearly explains the simultaneous role of nonlinear cubic term in the terrace formation. It is also demonstrated how ion beam can be used to tailor the wettability of glass surface and makes it hydrophobic in nature. Due to pattern formation, anisotropic hydrophobicity is observed showing an increasing trend owing to the magnification of the amplitude of nanopatterns developed on the surface.

Framework for Engineering of Spin Defects in Hexagonal Boron Nitride by Focused Ion Beams

AbstractHexagonal boron nitride (hBN) is gaining interest as a wide bandgap van der Waals host of optically active spin defects for quantum technologies. Most studies of the spin‐photon interface in hBN focus on the negatively charged boron vacancy (VB−) defect, which is typically fabricated by ion irradiation. However, the applicability and wide deployment of VB− defects is limited by VB− fabrication methods which lack robustness and reproducibility, particularly when applied to thin flakes (≲10 nm) of hBN. Here, two key factors are elucidated that underpin the formation and quenching of VB− centers by ion irradiation—density of defects generated in the hBN lattice and recoil‐implantation of foreign atoms into hBN. Critically, it is shown that the latter is extremely efficient at inhibiting the generation of optically‐active VB− centers. This is significant because foreign atoms such as carbon are commonplace on both the top and bottom surfaces of hBN during ion irradiation, in the form of hydrocarbon contaminants, polymer residues from hBN transfer methods, protective capping layers and substrates. Recoil implantation must be accounted for when selecting ion beam parameters such as ion mass, energy, fluence, incidence angle, and sputter/span yield, which are discussed in the context of a framework for VB− generation by high‐resolution focused ion beam (FIB) systems.

Super-heavy ion beams generated by a multi-PW femtosecond laser

The numerical investigations into the acceleration of superheavy ions driven by a multi-PW, 30 fs laser pulse with a peak intensity from 5 × 1022 to 2 × 1023 W/cm2 were carried out using an advanced 2D3V particle-in-cell code. The properties of laser-accelerated Au, Pb, Bi, and U ion beams, such as ionization and ion energy spectra, ion beam energies, angular distributions of the beam fluence, the ion pulse shapes, and peak intensities, were examined and compared. It was found that for a laser intensity of 1023 W/cm2, a common feature of the Au, Pb, Bi, and U ion beams was the dominance in the beam of Ne-like ions that carry the vast majority (≥90%) of the energy of all accelerated ions and have by far the highest mean and maximum ion energy. The Ne-like ion beams for Au, Pb, Bi, and U have almost identical angular fluence distributions and ion pulse shapes, as well as peak fluencies and intensities. However, the dependence of the parameters of the Ne-like ion beam on the laser intensity is different for ions with different masses. In the considered laser intensity range, the heaviest ions (U ions) ensured the achievement of the highest beam parameters, such as the mean and maximum ion energy, the ion beam energy, or the laser-to-ions energy conversion efficiency. The mono-charge superheavy ion beams demonstrated in this paper open the prospect for novel applications of heavy ions in high energy-density physics, nuclear physics, and possibly in other fields.

A Comparative Study of Gallium-, Xenon-, and Helium-Focused Ion Beams for the Milling of GaN.

The milling profiles of single-crystal gallium nitride (GaN) when subjected to focused ion beams (FIBs) using gallium (Ga), xenon (Xe), and helium (He) ion sources were investigated. An experimental analysis via annular dark-field scanning transmission electron microscopy (ADF-STEM) and high-resolution transmission electron microscopy (HRTEM) revealed that Ga-FIB milling yields trenches with higher aspect ratios compared to Xe-FIB milling for the selected ion beam parameters (30 kV, 42 pA), while He-FIB induces local lattice disorder. Molecular dynamics (MD) simulations were employed to investigate the milling process, confirming that probe size critically influences trench aspect ratios. Interestingly, the MD simulations also showed that Xe-FIB generates higher aspect ratios than Ga-FIB with the same probe size, indicating that Xe-FIB could also be an effective option for nanoscale patterning. Atomic defects such as vacancies and interstitials in GaN from He-FIB milling were suggested by the MD simulations, supporting the lattice disorder observed via HRTEM. This combined experimental and simulation approach has enhanced our understanding of FIB milling dynamics and will benefit the fabrication of nanostructures via the FIB technique.

Beam-plasma interaction in fast ignition nuclear fusion: Hot-spot properties and gains for different initial plasma temperatures

The main objective of this work is to characterize relevant properties of the hot spots obtained in the interaction between ion beams of V23+ and a spherical pure precompressed deuterium–tritium plasmas in the field of ion fast ignition scheme. In particular, we focus our analysis on the determination of the length, average temperature and maximum temperature (and its location) achieved by the hot spot as a function of the ion beam parameters (particle density and initial energy). Special attention is paid to central hot spots with characteristic lengths in the range 20–40 μm. Furthermore, the self-heating and ignition curves associated to the hot spots generated as well as the burning gain of the precompressed deuterium–tritium fuel are determined. This study is made for a wide range of the beam parameters in which the ignition of the hot spot is achieved and for precompressed deuterium–tritium plasma at 500 g cm3 and temperatures of 0.5, 1 and 5 keV.

Generation of pulsed proton beams in a vacuum diode with a passive anode

The paper presents the results of a study of a pulsed proton beam generated of in a diode with a metal anode (stainless steel, titanium, and copper) operating in bipolar-pulse mode. The experiments were carried out on the TEMP-6 accelerator (250–300 kV, 120 ns) with a focusing diode geometry in a mode of self-magnetic insulation of electrons. For analysis of the ion beam parameters, we used the infrared imaging diagnostics of the beam energy density (spatial resolution of 2 mm) and the time-of-flight diagnostics of the beam compositions (time resolution 1 ns). It was found that with continuous supply of hydrogen into a hollow anode (with holes on the working surface) and a hydrogen pressure in the diode chamber of 30–80 mPa, the proton content in the beam exceeds 80%. An increase in the first pulse duration leads to an increase in the ion current density up to 100 A/cm2 and the energy density at the focus up to 3 J/cm2. We analyzed various mechanisms of proton beam generation: ions acceleration from the gas plasma in the plasma erosion mode; ions acceleration from the explosive emission plasma of a metal anode the near-surface layer of which is saturated with metal hydrides (anode material). It was found that hydrogen embrittlement of the near-surface layer of the anode occurs during the injection of hydrogen, and during the explosive emission of electrons, part of the material is sprayed in the form of finely dispersed clusters.

Axial and radial space-charge effects in radiofrequency gas-filled low-pressure quadrupole ion guides

This paper presents theoretical and experimental study results of the space-charge (SC) effects in gas-filled radiofrequency ion guides, typically operating at ∼1 Pa gas pressures. A self-consistent Coulomb interaction simulation allows modeling the ion self-propulsion by the own SC, optionally supplemented by an external axial field. The simulations are accelerated with an improved collision model, combining the hard-sphere and polarization interaction models. Simulated ion beam parameters are consistent with the experimental measurements performed with an orthogonal accelerating time-of-flight mass spectrometer. The experimental and theoretical studies consistently demonstrate notable SC effects in ion guides, even at moderate ion currents in the sub-nA range. The effects become softer when using a weak ∼0.02 V/mm axial field. The efficiency of the ion guides improves with their miniaturization. The simulations and experiments demonstrate stronger beam compression for multiple-charged ions, even in the presence of SC effects, thus providing shorter turnaround times in orthogonal accelerators. The SC effects depend on the ion beam composition in the ion guides; the presence of light or multicharged ions strongly affects the ion motion of heavier species with a lower charge.

An investigation of luminescence properties of CaF2: Dy nanophosphor irradiated with gamma rays and low energy proton beams

This paper reports the luminescence properties of nanocrystalline calcium fluoride doped with dysprosium (CaF2: Dy). The nanophosphor has been synthesized by the chemical co-precipitation technique and the dopant concentration has been optimized at 0.3 mol% using thermoluminescence (TL) intensity emitted post 50Gy gamma dose irradiation of samples doped with different dopant concentrations. X-ray diffraction shows the formation of crystalline particles with an average size of 49.233 nm. Photoluminescence (PL) emission spectrum shows the characteristic peaks at 455 nm, 482 nm, 573 nm corresponding to 4I15/2 to 6H15/2, 4F9/2 to 6H15/2 and 4F9/2 to 6H13/2 Dy3+ transitions respectively. PL excitation spectrum shows a peak at 327 nm which corresponds to the Dy3+ transition of 6H15/2 to 4L19/2. Gamma (of 1.25 MeV) and low energy proton beam (of 30 keV) irradiated nanophosphor shows a variation in TL glow curve structure and peak position with an increase in radiation dose/fluence. However, the nanophosphor shows a wide linear dose response for 60Co gamma radiation in the range 10 Gy - 1.5 kGy and for low energy proton beam in the fluence range of 1012–1014 ions/cm2. Srim 2013 has been used to calculate the ion beam parameters including the range of protons in CaF2: Dy 0.3 mol%. The nanophosphor CaF2: Dy could be further investigated as a potential dosimeter for gamma rays and proton beam by studying its TL properties for different energies of these radiations.

Simulation and characterization of hot spots generated in deuterium–tritium plasma by fast quasi-monoenergetic ion beams

In this work, a model for the calculation of the temperature field reached by a compressed deuterium–tritium plasma heated by fast quasi-monoenergetic Gaussian ion beams is presented. Furthermore, from simulations performed on a wide range of ion beam parameters the interest in the field of ion fast ignition, an analysis of the properties of the generated hot spot is carried out. We focus the study on the influence of the parameters of the ion beam (particle density, initial mean energy and energy spread) on the spatial temperature field of the heated region and on some relevant parameters of the hot spot such as length, average temperature, maximum temperature and its position. The results presented in this work were obtained for fully ionized vanadium ion beam in a wide range of the beam parameters and for a compressed deuterium–tritium plasma at matter density and temperature given by 500gcm-3 and 1keV, respectively.

FEATURES OF VISUALIZATION OF THE THREE-DIMENSIONAL STRUCTURE OF MESOPOROUS PZT FILMS BY FIB-SEM NANOTOMOGRAPHY

A technique for studying the three-dimensional structure of porous lead zirconate titanate films by FIB-SEM-nanotomography is presented. Such quantitative characteristics as total porosity, specific surface area, and actual pore size (calculated using the local thickness method) have been obtained. According to the FIB-SEM-nanotomography data, the pore size is 77 ± 33 nm for the film with the PVP porogen and only 27 ± 6 nm for the film with the Brij76 porogen; the latter value is close to the limiting resolution for this method. The final 3D model is shown to be strongly influenced by the chosen ion-beam parameters during milling, which can be varied to obtain a structure without distortion or visualize the accumulation of pores at grain boundaries.

Atomistic Simulations of Defects Production under Ion Irradiation in Epitaxial Graphene on SiC

Using first‐principles and analytical potential atomistic simulations, production of defects in epitaxial graphene (EG) on SiC upon ion irradiation for ion types and energies accessible in helium‐ion microscope is studied. Graphene‐SiC systems consisting of the buffer (zero) graphene layer and SiC substrate, as well as one (monolayer) and two (bilayer) additional graphene layers, are focused on. The probabilities for single, double, and more complex vacancies to appear upon impacts of energetic ions in each graphene layer as functions of He‐ and Ne‐ion energies are calculated and the data are compared with those obtained for free‐standing graphene. The results indicate that the role of the substrate is minimal for He‐ion irradiation with energies above 5 keV, which can be associated with a low sputtering yield from this system upon ion irradiation, as compared with the common Si/SiO2 substrate. In contrast, SiC substrate has a significant effect on defect production upon Ne‐ion irradiation. The results can serve as a guide to the experiments on ion irradiation of EG to choose the optimum ion beam parameters for defect‐mediated engineering of such systems, for example, for creating nucleation centers to grow other 2D materials, such as h‐BN, on top of the irradiated EG.

Plasma characterization in CW and pulsed mode and its effect on beam current in 2.45 GHz ECR Ion source

Electron Cyclotron Resonance Ion Source (ECRIS) is used as a front end for Low Energy High Intensity Proton Accelerator (LEHIPA) at BARC. A 50 keV ECRIS is designed and developed for the proton ion beam for this accelerator. The key requirements of the ion source are beam current ∼ 10 – 15 mA and beam emittance ∼ 0.2 π mm-mrad. In the commissioning phase of LEHIPA, the ion source is operated in pulsed mode to mitigate the effect of thermal and radiation load. Measurements have been carried out to understand the behavior of pulsed plasma and its effect on ion beam. An Automated Langmuir Probe (ALP) and its associated circuit are designed and developed for this purpose. The ALP circuit consists of a voltage sweep generator, current sense circuit, and voltage sense circuit. The effect of microwave power and pulsed plasma duration on the plasma and the ion beam parameters have been studied. The plasma parameters are correlated with the beam parameters.

Ultra-intense laser-accelerated ion beams for high-gain inertial fusion: the effect of the ion mass on the beam properties

This paper presents the results of detailed numerical studies of the properties of ion beams generated by a laser from targets with various atomic numbers under conditions relevant for ion fast ignition (IFI) of inertial fusion. The interaction of a 200 kJ 1 ps infrared (1.05 μm) laser with Li, C, Al, Ti, Cu and CH2 flat targets with the same areal mass density was numerically simulated using an advanced 2D3V particle-in-cell code. For each target, a set of ion beam characteristics important for IFI was determined. A detailed quantitative comparison of the IFI-relevant parameters of Li, C, Al, Ti and Cu ion beams and the proton beam (from the CH2 target) was made. The laser-accelerated Cu ion beam was found to achieve significantly higher values of beam intensity, fluence and ‘useful’ energy (for IFI), having a smaller angular divergence and a narrower energy spectrum than the beam of light ions or protons. Thus, it is shown for the first time that laser-accelerated heavy ion beams can achieve IFI-relevant parameters higher than light ion or proton beams and can potentially meet IFI requirements.

Investigations of thermoluminescence characteristics of CaSiO3:Yb phosphor irradiated with gamma rays and carbon ion beam

In the present work, the thermoluminescence (TL) properties of Yb doped CaSiO3 phosphor exposed to gamma rays and carbon (C) ion beam have been reported. The phosphor has been synthesized using solid-state reaction method. The formation and surface morphology of the phosphor have been studied using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) respectively. The optical band gap of the phosphor is determined using UV–Visible spectroscopy. TL properties on Yb doped CaSiO3 phosphor irradiated with carbon ion beam has been reported first time. Different TL properties like TL glow curve, dose response, fading etc. have been investigated in detail. The TL glow curve of CaSiO3:Yb phosphor consists of two prominent glow peaks. Under gamma irradiation, the main dosimetric peak is centered at 141 °C and other peak is centered at 265 °C. The dose response behaviour has been studied in the range 10 Gy–1000 Gy. However, C ion beam irradiated phosphor also consists similar TL glow curve structure with glow peaks shifted towards high temperature side (approx. 50 °C). The dose response behaviour of C ion beam irradiated phosphor has been examined in the ion fluence range varying from 5 × 109–5 × 1012 ions/cm2. A track interaction model is used to explain the sublinearity at higher fluences of carbon ion beam. Different ion beam parameters have been analyzed using Monte-Carlo simulation-based SRIM code. A comparative TL study of the phosphor irradiated with gamma rays and carbon ion beam suggests that gamma irradiated phosphor has shown better TL properties such as high TL sensitivity, good linear dose response (10 Gy–500 Gy), stable TL glow curve structure and low fading. Various TL trapping parameters i.e. order of kinetics, activation energy and frequency factor have been calculated using Chen's peak shape method to analyze the nature of TL traps responsible for showing different behaviour of the phosphor towards both the radiations. Good TL properties of CaSiO3:Yb phosphor supports its possible use in gamma dosimetry.

Nanopattern Formation on Indium Phosphide Using Energetic Ions: An Overview with Various Ion Beam Parameters

Nanopattern formation using energetic ion beams has attracted interest due to their important applications in varied fields. Ion beams play a crucial role in the formation of nanostructured materials in different energy regimes. Low energy ions of a few Kiloelectron volt (keV) energy have been used for growing thin films using sputtering process. A few ~10 to 100s of keV ions are used for the growth of nanopatterns (nanodots or nanoripples) through self-assembly or self-organization. Such pattern formation depends hugely on ion beam parameters such as angle of incidence of the beam, ion fluence, ion energy, and target material properties. Thereby, tuning the ion beam parameters, the desired shape and size of the nanopatterns may be achieved on wide variety of substrates. In this paper, effect of the above-mentioned ion beam parameters, especially, on Indium Phosphide (InP), is reported from our earlier studies. Further, the correlations have been made where such patterns have been used for various applications.

Effects of axial magnetic field in a magnetic multipole line cusp ion source

Experiments have been performed to study the effects of axial magnetic field on plasma and ion beam parameters in a magnetic multipole line cusp ion source. Studies performed on ring cusp and Kaufmann type ion sources suggest that the axial component of magnetic field may help in improving the ion extraction current at a low discharge power. The line cusps ion sources have been used since long to produced uniform beams, however, they lack axial component of the magnetic field. These ion sources generally suffer from low efficiency possibly due the absence of axial magnetic field. In this work, an additional magnetic coil is added at various axial positions between the back-plate and the plasma grid of the multipole line cusp ion source. We have investigated the effects of axial magnetic field on the discharge efficiency and source parameters like beam current and uniformity in the multipole line cusp ion source. The beam profiles are obtained using an eleven-channel faraday cup array to estimate the effects of the axial magnetic field on beam uniformity and divergence. Initial studies suggest a reduction of beam divergence with increasing axial magnetic field. A significant rise in the beam current and the discharge current is also observed when the axial magnetic field is increased. Particle trajectory simulation using the CST-Studio suite is utilised in understanding the role of confinement of primary electrons behind the improved performance of the ion source.

Laser ion source for semiconductor applications

Carbon implantation can be effectively used for axial minority charge carriers’ lifetime control in various silicon bulk and epitaxial planar structures. When carbon is implanted, more stable recombination centres are formed and silicon is not doped with additional impurities, as for example, when irradiated with protons or helium ions. Economically, such a process competes with alternative methods, and is more efficient for obtaining small lifetimes (several nanoseconds). I-3 ion injector with laser-plasma ion source at Institute for theoretical and experimental physics (ITEP) is used as ion implanter in semiconductors. The ion source uses pulsed CO2 laser setup with radiation-flux density of 1011 W/cm2 at target surface. The ion source produces beams of various ions from solid targets. The generated ion beam is accelerated in the two gap RF resonator at voltage of up to 2 MV per gap. Resulting beam energy is up to 4 MV per charge. Parameters of carbon ion beam generated and used for semiconductor samples irradiation during experiments for axial minority charge carriers lifetime control in various silicon bulk and epitaxial planar structures are presented.

Deep-Learning-Assisted Focused Ion Beam Nanofabrication.

Focused ion beam (FIB) milling is an important rapid prototyping tool for micro- and nanofabrication and device and materials characterization. It allows for the manufacturing of arbitrary structures in a wide variety of materials, but establishing the process parameters for a given task is a multidimensional optimization challenge, usually addressed through time-consuming, iterative trial-and-error. Here, we show that deep learning from prior experience of manufacturing can predict the postfabrication appearance of structures manufactured by focused ion beam (FIB) milling with >96% accuracy over a range of ion beam parameters, taking account of instrument- and target-specific artifacts. With predictions taking only a few milliseconds, the methodology may be deployed in near real time to expedite optimization and improve reproducibility in FIB processing.

X-ray Photoelectron Spectroscopy Equipped with Gas Cluster Ion Beams for Evaluation of the Sputtering Behavior of Various Nanomaterials

The selection of ion-beam species and parameters for depth profiling requires experience to obtain accurate depth information and an efficient sputter rate on diverse samples. Sputter damage that causes changes in the chemical state and composition should be avoided. Monoatomic ion-beam sources are commonly utilized for the rapid sputtering of metals and inorganics, but sputter damage to highly oxidized metal oxides and organics is well-known. Cluster ion beams have become popular in recent years for soft materials because of their capability for low damage to organics, but sputter yields of metal and inorganic materials are very low. Currently, the material properties and structures of semiconductor devices have become more complicated because of rapid technical development. Thus, it is necessary to explore more sputtering methods for samples with hybrid architecture that contain metals/inorganics/organics together. Recently, gas cluster ion beams (GCIBs) with small cluster sizes were considered to be one of the methods with the advantages of both monatomic ion beams and conventional large-cluster GCIBs (>Ar2000+). A smaller-cluster GCIB results in higher energy per atom with a sputtering behavior similar to that of the monatomic ion beam and leads to enhancement of the sputter yield in metal and inorganic layers. However, the discussion of the cluster size selection for X-ray photoelectron spectroscopy (XPS) chemical state analysis during depth profiling is rather limited. In this work, a GCIB cluster measurement kit is developed and installed in an XPS system. The actual distribution of the cluster size of each GCIB setting can be measured before depth profiling. Depth profiling using GCIBs with a series of cluster sizes is performed to examine the sputter yield and evaluate the sputter effect on various organic, inorganic, and hybrid nanomaterials. The results also show the different sputtering behaviors of GCIBs with different cluster sizes (Ar500–2000+).