Primary Ion Energy Research Articles

Heteroepitaxial growth of Ga2O3 thin films on Al2O3(0001) by ion beam sputter deposition

Deposition of epitaxial oxide semiconductor films using physical vapor deposition methods requires a detailed understanding of the role of energetic particles to control and optimize the film properties. In the present study, Ga2O3 thin films are heteroepitaxially grown on Al2O3(0001) substrates using oxygen ion beam sputter deposition. The influence of the following relevant process parameters on the properties of the thin films is investigated: substrate temperature, oxygen background pressure, energy of primary ions, ion beam current, and sputtering geometry. The kinetic energy distributions of ions in the film-forming flux are measured using an energy-selective mass spectrometer, and the resulting films are characterized regarding crystalline structure, microstructure, surface roughness, mass density, and growth rate. The energetic impact of film-forming particles on the thin film structure is analyzed, and a noticeable decrease in crystalline quality is observed above the average energy of film-forming Ga+ ions around 40 eV for the films grown at a substrate temperature of 725 °C.

Disequilibrium oxygen isotope distribution among aqueously altered minerals in Ryugu asteroid returned samples

AbstractOxygen 3‐isotope ratios of magnetite and carbonates in aqueously altered carbonaceous chondrites provide important clues to understanding the evolution of the fluid in the asteroidal parent bodies. We conducted oxygen 3‐isotope analyses of magnetite, dolomite, and breunnerite in two sections of asteroid Ryugu returned samples, A0058 and C0002, using a secondary ion mass spectrometer (SIMS). Magnetite was analyzed by using a lower primary ion energy that reduced instrumental biases due to the crystal orientation effect. We found two groups of magnetite data identified from the SIMS pit morphologies: (1) higher δ18O (from 3‰ to 7‰) and ∆17O (~2‰) with porous SIMS pits mostly from spherulitic magnetite, and (2) lower δ18O (~ −3‰) and variable ∆17O (0‰–2‰) mostly from euhedral magnetite. Dolomite and breunnerite analyses were conducted using multi‐collection Faraday cup detectors with precisions ≤0.3‰. The instrumental bias correction was applied based on carbonate compositions in two ways, using Fe and (Fe + Mn) contents, respectively, because Ryugu dolomite contains higher amounts of Mn than the terrestrial standard. Results of dolomite and breunnerite analyses show a narrow range of ∆17O; 0.0‰–0.3‰ for dolomite in A0058 and 0.2‰–0.8‰ for dolomite and breunnerite in C0002. The majority of breunnerite, including large ≥100 μm grains, show systematically lower δ18O (~21‰) than dolomite (25‰–30‰ and 23‰–27‰ depending on the instrumental bias corrections). The equilibrium temperatures between magnetite and dolomite from the coarse‐grained lithology in A0058 are calculated to be 51 ± 11°C and 78 ± 14°C, depending on the instrumental bias correction scheme for dolomite; a reliable temperature estimate would require a Mn‐bearing dolomite standard to evaluate the instrumental bias corrections, which is not currently available. These results indicate that the oxygen isotope ratios of aqueous fluids in the Ryugu parent asteroid were isotopically heterogeneous, either spatially, or temporary. Initial water ice accreted to the Ryugu parent body might have ∆17O > 2‰ that was melted and interacted with anhydrous solids with the initial ∆17O < 0‰. In the early stage of aqueous alteration, spherulitic magnetite and calcite formed from aqueous fluid with ∆17O ~ 2‰ that was produced by isotope exchange between water (∆17O > 2‰) and anhydrous solids (∆17O < 0‰). Dolomite and breunnerite, along with some magnetite, formed at the later stage of aqueous alteration under higher water‐to‐rock ratios where the oxygen isotope ratios were nearly at equilibrium between fluid and solid phases. Including literature data, δ18O of carbonates decreased in the order calcite, dolomite, and breunnerite, suggesting that the temperature of alteration might have increased with the degree of aqueous alteration.

Proton irradiation-induced cracking and microstructural defects in UN and (U,Zr)N composite fuels

Proton irradiation with a primary ion energy of 2 MeV was used to simulate radiation damage in UN and (U,Zr)N fuel pellets. The pellets, nominally at room temperature, were irradiated to peak levels of 0.1, 1, 10 dpa and 100.0 dpa resulting in a peak hydrogen concentration of at most 90 at. %. Microstructure and mechanical properties of the samples were investigated and compared before and after irradiation. The irradiation induced an increase in hardness, whereas a decrease in Young’s modulus was observed for both samples. Microstructural characterization revealed irradiation-induced cracking, initiated in the bulk of the material, where the peak damage was deposited, propagating towards the surface. Additionally, transmission electron microscopy was used to study irradiation defects. Dislocation loops and fringes were identified and observed to increase in density with increasing dose levels. The high density of irradiation defects and hydrogen implanted are proposed as the main cause of swelling and consequent sample cracking, leading simultaneously to increased hardening and a decrease in Young's modulus.

ToF-SIMS analysis of ultrathin films and their fragmentation patterns.

Organic thin films are of great interest due to their intriguing interfacial and functional properties, especially for device applications such as thin-film transistors and sensors. As their thickness approaches single nanometer thickness, characterization and interpretation of the extracted data become increasingly complex. In this study, plasma polymerization is used to construct ultrathin films that range in thickness from 1 to 20 nm, and time-of-flight secondary ion mass spectrometry coupled with principal component analysis is used to investigate the effects of film thickness on the resulting spectra. We demonstrate that for these cross-linked plasma polymers, at these thicknesses, the observed trends are different from those obtained from thicker films with lower degrees of cross-linking: contributions from ambient carbon contamination start to dominate the mass spectrum; cluster-induced nonlinear enhancement in secondary ion yield is no longer observed; extent of fragmentation is higher due to confinement of the primary ion energy; and the size of the primary ion source also affects fragmentation (e.g., Bi1 versus Bi5). These differences illustrate that care must be taken in choosing the correct primary ion source as well as in interpreting the data.

INFLUENCE OF DOPING WITH CARBON AND NITROGEN ON THE PHOTOACTIVITY OF TiO2 THIN FILMS OBTAINED WITH MePIIID

Titanium dioxide is well known as a photoactive material activated under ultraviolet irradiation. It is either employed as a photocatalyst or it exhibits superhydrophilic behavior after obtaining reduced surface energy under illumination used for self-cleaning or anti-fogging surfaces. For increasing the reactivity of thin films under solar illumination, a reduced band gap is desired. Doping with transition metals or nitrogen has been reported in the literature. However, the incorporation of nitrogen into a growing film is a much more complex process that is presently not completely understood. TiO2 thin layers were produced by metal plasma immersion ion implantation and deposition at room temperature at a pulse voltage of 0–5 kV and a duty cycle of 9 % for an apparently amorphous layer. An auxiliary rf plasma source was employed to increase the growth rate at low gas flow ratios. By adjusting the geometry between the incident ion beam, sputter target and substrate independently of the primary ion energy and species, a controlled deposition of samples was possible. Conventional ion implantation was employed to implant either carbon or nitrogen ions below the surface for bandgap engineering. The resulting thin films were subsequently investigated for optical properties, stoichiometry, structural properties, surface topography and photoactivity.

Depth profiling of Cr-ITO dual-layer sample with secondary ion mass spectrometry using MeV ions in the low energy region

This work explores the possibility of depth profiling of inorganic materials with Megaelectron Volt Secondary Ion Mass Spectrometry using low energy primary ions (LE MeV SIMS), specifically 555 keV Cu2+, while etching the surface with 1 keV Ar+ ions. This is demonstrated on a dual-layer sample consisting of 50 nm Cr layer deposited on 150 nm In2O5Sn (ITO) glass. These materials proved to have sufficient secondary ion yield in previous studies using copper ions with energies of several hundred keV. LE MeV SIMS and keV SIMS depth profiles of Cr-ITO dual-layer are compared and corroborated by atomic force microscopy (AFM) and time-of-flight elastic recoil detection analysis (TOF-ERDA). The results show the potential of LE MeV SIMS depth profiling of inorganic multilayer systems in accelerator facilities equipped with MeV SIMS setup and a fairly simple sputtering source.

Properties of gallium oxide thin films grown by ion beam sputter deposition at room temperature

Gallium oxide thin films were grown by ion beam sputter deposition (IBSD) at room temperature on Si substrates with systematically varied process parameters: primary ion energy, primary ion species (O2+ and Ar+), sputtering geometry (ion incidence angle α and polar emission angle β), and O2 background pressure. No substrate heating was applied because the goal of these experiments was to investigate the impact of the energetic film-forming species on thin film properties. The films were characterized with regard to film thickness, growth rate, crystallinity, surface roughness, mass density, elemental composition and its depth profiles, and optical properties. All films were found to be amorphous with a surface roughness of less than 1 nm. The stoichiometry of the films improved with an increase in the energy of film-forming species. The mass density and the optical properties, including the index of refraction, are correlated and show a dependency on the kinetic energy of the film-forming species. The ranges of IBSD parameters, which are most promising for further improvement of the film quality, are discussed.

Properties of secondary ions in ion beam sputtering of Ga2O3

The energy distributions of secondary ions for the ion beam sputtering of a Ga2O3 target using O2+ and Ar+ ions are measured in dependence on various process parameters using energy-selective mass spectrometry. The process parameters include sputtering geometry (ion incidence angle α, polar emission angle β, scattering angle γ), the energy of incident ions Eion, and the background pressure of O2. The main secondary ion species are identified to be Ga+, O+, O2+, and, when argon is used as a process gas, Ar+. The changes in the sputtering geometry and the primary ion energy have the most impact on the energy distributions of secondary Ga+ and O+ ions, giving control over the high-energy tail, which is attributed to anisotropy effects in sputtering. The formation of O2+ ions is attributed to collisions with background gas molecules, as their energy distributions are not influenced by the sputtering geometry or the primary ion energy. The increase of the O2 pressure leads to a minor decrease of the energy of Ga+ ions due to collisions with the background gas particles. The use of primary Ar+ ions with O2 background pressure does not show any specific effect on energy distributions of Ga+, O+, and O2+ ions except for the case without additional O2 background. In the latter case, much fewer O+ and O2+ ions are produced indicative of oxygen depletion of the surface due to preferential sputtering of oxygen. At all considered O2 pressures, the energy distributions of Ar+ ions have a high-energy peak, attributed to direct scattering events. The trends in experimental data show qualitative agreement to simulations using the Monte Carlo code SDTrimSP.

High Mass Resolution Multireflection Time-of-Flight Secondary Ion Mass Spectrometer.

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is popular because of its advantages of parallel m/z detection and less damage for unknown or rare samples compared to sector field instruments. However, the mass resolving power of conventional TOF-SIMS is limited by its relatively large energy spread and primary ion pulse width. In this work, a high mass resolution multireflection time-of-flight secondary ion mass spectrometer (MR-TOF-SIMS) was designed and constructed. Compared with conventional TOF-SIMS, the ion flight path of the MR-TOF-SIMS was extended from meters to subkilometers, and the mass resolving power reached to 87000 after an 80 cycles flight. A pair of symmetrically arranged ion orthogonal injection/ejection deflectors, which could eliminate the influence of fringing field and remove ions with a large energy spread, were proposed to further improve the mass resolving power in fewer flight cycles. A zircon standard sample sputtered by a 10 keV O2- beam was used to demonstrate the performance of the MR-TOF-SIMS instrument. As a result, the mass resolving power was up to 30000 only after 22 flight cycles. The 92Zr+ peak was significantly separated from the mass interference peaks of 91ZrH+, 90ZrH2+, 13CC6H7+, and C7H8+. The mass accuracies of Zr ions and their hydrides were better than 1.2 ppm. An ion transmission efficiency over 40% was achieved after 115 cycles.

MeV TOF SIMS Analysis of Hybrid Organic/Inorganic Compounds in the Low Energy Region.

The low energy range (a few 100 keV to a few megaelectronvolts) primary ion mode in MeV secondary ion mass spectrometry (MeV SIMS) and its potential in exploiting the capabilities of conventional (keV) SIMS and MeV SIMS simultaneously were investigated. The aim is to see if in this energy range of both types of materials, inorganic and organic, can be simultaneously analyzed. A feasibility study was conducted, first by analyzing the dependence of secondary ion yields in indium tin oxide (ITO, In2O5Sn) and leucine (C6H13NO2) on various primary ion energies and charge states of a Cu beam, within the scope of equal influence of electronic and nuclear stopping. Expected behavior was observed for both targets (mainly nuclear sputtering for ITO and electronic sputtering for leucine). MeV SIMS images of samples containing separate regions of Cr and leucine were obtained using both keV and MeV primary ions. On the basis of the image contrast and measured data, the benefit of a low energy beam is demonstrated by Cr+ intensity leveling with leucine [M + H]+ intensity, as opposed to a significant contrast at a higher energy. It is estimated that, by lowering the energy, the leucine [M + H]+ yield efficiency lowers roughly 20 times as a price for gaining about 10 times larger efficiency of Cr+ yield, while the leucine [M + H]+ yield still remains sufficiently pronounced.

Nonlinear effects in low-energy ion sputtering of solids

In this paper, we demonstrate that the sputtering of solids by ions of low (<30 keV) and even ultralow energies (<2 keV) is accompanied by nonlinear effects. These nonlinear effects are the result of heating a significant part of the cascades of collisions above the effective melting temperature of the material with the formation of local melts or “thermal spots” (a special case of the thermal spike regime). Nonlinear effects should primarily be observed in dense targets irradiated by heavy and cluster ions. In this paper, the question of the lifetime of such spots and their effect on the emission of secondary particles and the formation of specific surface topography is examined in detail. Another important assumption of the model is the existence of an intermediate ion sputtering regime, in that both linear cascades and thermal spots can exist simultaneously. A phenomenological model based on the effect of a rapid decrease in the cascade volume with a monotonic decrease in the energy of primary ions below 3 keV, which leads to the formation of thermal spots at ultralow energies (<2 keV), is also proposed. The suggested thermal spot model allows us to explain several experimental data that have not yet been explained in the framework of the traditional sputtering models. In particular, a simple explanation is given for the formation of pores in the surface layer during implantation and the formation of a relief on an ion-bombarded surface such as nanodots, pits (holes), and in the form of a foam-like surface. The small stationary concentration of cesium on the surface of the target sputtered by low-energy cesium ions is also explained.

Dependence of Megaelectron Volt Time-of-Flight Secondary Ion Mass Spectrometry Secondary Molecular Ion Yield from Phthalocyanine Blue on Primary Ion Stopping Power.

Time-of-flight secondary ion mass spectrometry (TOF SIMS) is a well-established mass spectrometry technique used for the chemical analysis of both organic and inorganic materials. In the last ten years, many advances have been made to improve the yield of secondary molecular ions, especially those desorbed from the surfaces of organic samples. For this reason, cluster ion beams with kiloelectron volt energies for the excitation were mostly used. Alternatively, single-ion beams with megaelectron volt energies can be applied, as was done in the present work. It is well-known that a secondary molecule/ion yield depends strongly on the primary ion stopping power, but the nature of this dependence is not completely clear. Therefore, in the present work, the secondary ion yield from the phthalocyanine blue (C32H16CuN8, organic pigment) was measured for the various combinations of ion masses, energies, and charge states. Measured values were compared with the existing models for ion sputtering. An increase in the secondary yield with the primary ion energy, electronic stopping, velocity, and charge state was found for different types of primary ions. Although this general behavior is valid for all primary ions, there is no single parameter that can describe the measured results for all primary ions at once.

Properties of secondary particles for ion beam sputtering of silicon using low-energy oxygen ions

The properties of secondary particles for sputtering silicon with primary low-energy oxygen ions were investigated with dependence on the primary ion energy Eion and geometric parameters (ion incidence angle, polar emission angle, and scattering angle). The mass and energy distributions of the secondary particles were measured by energy-selective mass spectrometry. The experimental results were compared with simulations using the Monte Carlo code sdtrimsp and with calculations based on a simple elastic binary collision model. The main secondary ion species were found to be O+, O2+, Si+, and SiO+. Their energy distribution functions depend on the primary ion energy Eion and the scattering angle γ. For O+, Si+, and SiO+ ions, a decreasing scattering angle γ or an increasing primary ion energy Eion leads to a pronounced feature in the high-energy part of the distributions. The energy distributions of the secondary O2+ ions show hardly any changes with regard to the primary ion energy or the scattering angle γ. In the case of the O+ ions, the energy distribution appears to reflect several direct scattering channels, which could be associated with the primary ion energy Eion, and half of the ion energy Eion/2. The present experimental results are compared with previous investigations for the sputtering of Si with the noble gas ions, such as Ne+, Ar+, and Xe+.

Angular dependence of nanoparticle generation in the matrix assembly cluster source

The matrix assembly cluster source (MACS) represents a bridge between conventional instruments for cluster beam deposition (CBD) and the level of industrial production. The method is based on Ar+ ion sputtering of a pre-condensed Ar-M matrix (where M, is typically a metal such as Ag). Each Ar+ ion produces a collision cascade and thus the formation of metal clusters is in the matrix, which are then sputtered out. Here we present an experimental and computational investigation of the cluster emission process, specifically its dependence on the Ar+ ion angle of incidence and the cluster emission angle. We find the incidence angle strongly influences the emerging cluster flux, which is assigned to the spatial location of the deposited primary ion energy relative to the cluster into the matrix. We also found an approximately constant angle between the incident ion beam and the peak in the emitted cluster distribution, with value between 99° and 109°.

Detection of lithium in scalp hair by time-of-flight secondary ion mass spectrometry with high energy (MeV) primary ions

The application of MeV-SIMS is presented for the detection and mapping of lithium in chemically unprocessed, longitudinally sectioned scalp hair.

Features of spectra of low-energy neon ions scattered from gallium phosphide

Using mass-resolved ion scattering spectrometry, spectra of Ne+ ions scattered at an angle of 120° from the surface of GaP in the energy range of 0.4–1.96 keV have been studied in detail. In the spectra, in addition to the peaks of elastic binary Ne+/P and Ne+/Ga collisions, the peak of sputtered neon ions has been found, as well as the wide peak (a “hump”), the energy of which slightly depends on the energy of primary ions and the intensity considerably increases with an increase in this energy. In our opinion, the main contribution to this peak is made by neon ions that undergo multiple collisions with gallium and phosphorus atoms on the surface and deeper layers of the sample and keep their charge due to reionization processes.

Lipid specific molecular ion emission as a function of the primary ion characteristics in TOF-SIMS.

In the present work, the emission characteristics of lipids as a function of the primary ion cluster size and energy were studied using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Characteristic fragmentation patterns for common lipids are described, and changes in secondary ion (SI) yields using various primary ion beams are reported. In particular, emission characteristics were studied for pairs of small polyatomic and nanoparticle primary ion beams (e.g., Bi3+ versus Ar1000+ and Au3+ versus Au400+4) based on the secondary ion yield of characteristic fragment and intact molecular ions as a function of the lipid class. Detailed descriptions of the fragmentation patterns are shown for positive and negative mode TOF-SIMS. Results demonstrate that the lipid structure largely dictates the spectral presence of molecular and/or fragment ions in each ionization mode due to the localization of the charge carrier (head group or fatty acid chain). Our results suggest that the larger the energy per atom for small polyatomic projectiles (Bi3+ and Au3+), the larger the SI yield; in the case of nanoparticle projectiles, the SI increase with primary ion energy (200-500 keV range) for Au400+4 and with the decrease of the energy per atom (10-40 eV/atom range) for Arn=500-2000+ clusters. The secondary ion yield of the molecular ion of lipids from a single standard or from a mixture of lipids does not significantly change with the primary ion identity in the positive ion mode TOF-SIMS and slightly decreases in the negative ion mode TOF-SIMS.

Examination of ion beam induced damage on polymer surface using Ar clusters

The damage of polymer surfaces caused by the high energy primary ion beams of TOF‐SIMS was examined using Ar cluster ions. Polymer damage, the damage of secondary ions detected from the polystyrene surface and the damage layer formed by the Bi3 primary ion beam have previously been studied. In this study, the damage observed in the secondary ions was studied by using Ar cluster primary ions. The secondary ions were mainly classified into two types, ions reflecting the polystyrene structure and cyclized ions, generated by excessive energy, which are not useful for qualitative analysis. The layer damaged by irradiation of the Bi3 primary ion regarding PS samples was confirmed using Ar cluster sputtering beams. The depth of the layer that has chemical damage in the PS main chain caused by 30 kV Bi3++ (ion dose: 5 × 1012 ions/cm2) irradiation was approximately 50–60 nm. The Ar cluster ion sputter rate in PS decreases with the Bi3 ion irradiation. Micro PS particles that are not able to be detected by a conventional TOF‐SIMS measurement can be effectively analyzed by accumulating the secondary ions over the static limit using Ar cluster sputtering. Copyright © 2016 John Wiley & Sons, Ltd.

Characteristics of flows of energetic atoms reflected from metal targets during ion bombardment

Particle number and energy reflection coefficients for energetic neutralized gas ions (Ar and O atoms) backscattered from metal targets during ion bombardment have been calculated using TRIM code. The energy distributions of reflected atoms are computed, too, and their dependence on the primary ion energy and the angle of ion incidence is determined. The obtained data confirm the possibility of employing energetic atoms reflection for generation of high energy neutral beams and point out to take this phenomenon into account under analysis of the ion technology for coating deposition.

Low-temperature diffusion of implanted sodium in silicon

We have studied the low-temperature diffusion of sodium atoms implanted (at primary ion energy E = 300 keV to total doses within Φ = 5 × 1014–3 × 1015 cm–2) in single-crystalline silicon grown by the method of float-zone melting (fz-Si) with low oxygen concentration N O and by the Czochralski method in the presence of magnetic field (mCz-n-Si and mCz-p-Si) with N O ≈ 5 × 1017 cm–3. The diffusion was studied at annealing temperatures within T ann = 500–420°C for periods of time t ann = 72–1000 h. It is established that the temperature dependence of the diffusion coefficient D(103/T) of sodium in fz-Si in a broad range of T ann = 900–420°C obeys the Arrhenius law with E fz = 1.28 eV and D 0 = 1.4 × 10–2 cm2/s. The same parameters are valid for the implanted sodium diffusion in mCz-Si in the interval of T ann = 900–700°C. However, at lower temperatures, the values of D in mCz-Si are lower than to those in fz-Si, which is related to the formation of more complicated Na–O n (n > 1) complexes in the former case. Estimation of the diffusion activation energy of these complexes yields ΔE ≈ 2.3 eV.