Incident Ion Beam Research Articles

Anomalous enhancement of focused ion beam etching by single raster propagating toward ion beam at glancing incidence

Focused ion beam (FIB) sample preparation for electron microscopy often requires large volumes of materials to be removed. Prior efforts to increase the rate of bulk material removal were mainly focused on increasing the primary ion beam current. Enhanced yield of etching at glancing ion beam incidence is known but has not found widespread use in practical applications. In this study, etching at glancing ion beam incidence was explored for its advantages in increasing the rate of bulk material removal. Anomalous enhancement of material removal at glancing angles of ion beam incidence was observed with single-raster etching in along-the-slope direction with toward-FIB direction of raster propagation. Material removal was inhibited in an away-from-FIB direction of raster propagation. The effects of glancing angles and ion doses on depth of cut and volume of removed materials were also recorded. We demonstrated that the combination of single-raster FIB etching at glancing incidence in along-the-slope direction with toward-FIB raster propagation and a “staircase” type of etching strategy holds promise for reducing the processing time for bulk material removal in FIB sample preparation applications.

An offline prediction of nanoscale ripples propagation under ion irradiation: A correlation between ripples velocity and surface erosion rate

An offline measurement of surface ripples propagation has been proposed using sequential ion beam irradiation approach. First, the ripple patterns were grown on Si (100) using 100 keV Ar+ at a fluence of 9 × 1017 ions/cm2 and then subsequent second stage irradiation was performed on partially masked rippled surface to study the ripple's propagation and surface erosion. Offline atomic force microscopy (AFM) study shows that with increase in fluence from 3 × 1017 ions/cm2 to 7 × 1017 ions/cm2, in second stage irradiation, the ripples are found to propagate along the projection of the ion beam's incident direction onto the surface. This observation of ripples propagation contradicts several existing models for ion-beam-induced ripple development. Furthermore, surface erosion rate due to sputtering was measured using stylus profilometer. A prediction of relation “v ~0.75 vo” between ripple's propagation velocity (v) and surface erosion rate (vo) shows the importance of Navier-Stokes viscous flow in near surface layer for the evolution of ripple patterns under ion beam irradiation (IBI).

Investigation for Low-Rate Fenceless Al Etching Applied in Fabrication of Superconducting Circuits

Ion beam etching (IBE) is introduced in the fabrication process developed from Nb03 in SIMIT, for the etching of Al-AlOx layer. However, we found that IBE creates fences at the edges of etched profiles because of redeposition of the Al. To solve this problem, we systematically investigated the yield of fenceless patterns and the junction quality as a function of ion beam incidence angle. The yield increases as the incidence angle decreases, 0° causing the least fence formation. The yield dependence was explained by a fence formation model developed from a two-dimensional redeposition algorithm. Given that the un-etched foots due to the shadow effect become visible as angle decreases, the optimal condition is finally set to be 400 eV with incidence angle of 10°. Nb/Al-AlOx/Nb junctions fabricated by Al-AlOx layer etching at incidence angle of 10° showed good junction quality with a low subgap leakage current. We could also obtain a high yield of shunted and unshunted Nb/Al-AlOx/Nb junctions with the minimum size of 1.4 μm in diameter on 4-inch Si wafers. These results prove the feasibility to achieve fabrication without anodization process and patterning of Al to improve the reliability.

Highly ordered silicide ripple patterns induced by medium-energy ion irradiation

We study the nanopatterning of silicon surfaces under near-normal 40-keV ${\mathrm{Ar}}^{+}$ sputtering with simultaneous Fe oblique codeposition. The ion-beam incidence was kept at 15\ifmmode^\circ\else\textdegree\fi{}, for which no pattern is produced in the absence of metal incorporation. Morphological and compositional analyses were performed by atomic force microscopy, in its morphological and electrical modes, Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, scanning Auger, as well as transmission and scanning electron microscopy. Initially, nanodot structures randomly emerge, which, with increasing ion fluence, become progressively aligned along the perpendicular direction to the Fe flux. With increasing fluence, they coalesce, leading to a ripple pattern. The pattern dynamics and characteristics are faster and enhanced, respectively, as the distance to the metal source decreases (i.e., as the metal content increases). For the highest metal flux, the ripples can become rather large (up to 18 \ensuremath{\mu}m) and straighter, with few defects, and a pattern wavelength close to 500 nm, while keeping the surface roughness close to 15 nm. Furthermore, for a fixed ion fluence, the pattern order is improved for higher metal flux. In contrast, the pattern order enhancement rate with ion fluence does not depend on the metal flux. Our experimental observations agree with the predictions and assumptions of the model by Bradley [R. M. Bradley, Phys. Rev. B 87, 205408 (2013)] Several compositional and morphological studies reveal that the ripple pattern is also a compositional one, in which the ripple peaks have a higher iron silicide content, in agreement with the model. Likewise, the ripple structures develop along the perpendicular direction to the Fe flux, and the pattern wavelength increases as the metal flux decreases with a behavior qualitatively consistent with the model predictions.

Characterization of optical waveguide in chalcogenide glass formed by helium ion implantation

In this work, an optical waveguide in the chalcogenide glass (80GeS2–15Ga2S3–5Sb2S3) is fabricated for the first time and its optical properties are investigated. A one-dimensional chalcogenide waveguide structure has been formed by 550 keV He+ ion implantation with a dose of 4 × 1016 ions/cm2 at room temperature. The effective refractive indices of the guided modes at the wavelength of 632.8 nm were measured with the aid of the Model 2010 Prism Coupler system. The refractive index profile, a critical factor in the analysis of waveguide structure, was reconstructed by the reflectivity calculation method. It was found that a positive change of refractive index occurred in the waveguide region, and an optical barrier with decreased refractive index was built at the end of the ion trajectory, i.e., producing a type of “well + barrier” structure. The SRIM 2013 program was utilized to display the profile of the energy loss versus the penetrated depth when the incident ion beam implanted. The near-field intensity distribution for the fundamental mode along the TE polarization was simulated through the finite-difference beam propagation method. From our experiments, these data provide a great deal of useful information about the manufacture of the chalcogenide waveguide structure.

Ar+-sputtered Ge (001) surface nanostructuring at target temperature above the recrystallization threshold

Nanoscale pattern formation on Ge (001) surface by 500 eV Ar+ bombardment has been studied for a wide range of ion incidence angles at a temperature of 300° C. In the angular regime 0° to 65°, a fourfold symmetric topography forms which shows a remarkable transition into highly regular one-dimensional asymmetric pattern at grazing incidences, known as perpendicular mode ripples. The four-fold symmetric patterns are found to retain their symmetry under the concurrent substrate rotation during sputtering, while the ripples show degeneration into hole structure with a weak fourfold symmetric pattern. The dynamics of the observed patterns has also been investigated in a wide range of ion fluence from 1 × 1017 to 1 × 10 20 ions cm−2. The square topographies are found to be determined by Ehrlich–Schwoebel barrier induced diffusion bias driven growth process, whereas, the ripple formation implies the role of incidence ion beam direction.

Irradiation induced elongation of Fe nanoparticles embedded in silica films

ABSTRACT Irradiation with swift heavy ions causes the deformation of Ferric nanoparticles in direction of the ion beam. Fe nanoparticles with mean diameter of about 20 nm were prepared by gas flow sputtering and subsequently confined within silica films. Two silica films wherein two different densities of Fe nanoparticles are encapsulated were irradiated with 50 MeV Ag ions with fluences of few 1014 ions.cm−2 at 300 K and normal incidence. Transmission electron microscopy analysis shows that the spherical Fe nanoparticles are deformed into prolate nanorods aligned in direction of the incident ion beam. The depth distribution profiles of irradiated particles reveal the presence of a critical fluence above which the elongation kinetics becomes dependent on the nanoparticles density. Analysis indicates that for the lower density particles, a saturation length is reached under irradiation to fluence between 3–4 × 1014 ions.cm−2. However, for the higher density, collective growth into aligned nanowires is presumed to take place. Hysteresis curves of the saturation magnetization and coercivity indicate an increasing magnetic anisotropy, which can be correlated with the deformation of nanoparticles in the direction of the ion beam.

Monte Carlo Investigation of the Depth-dose Profile of Proton Beams and Carbon Ions in Water, Skeletal Muscle, Adipose Tissue, and Cortical Bone for Hadron Therapy Applications

In this study, the depth-dose profile in water, skeletal muscle, adipose tissue, and cortical bone irradiated using incident beams of protons and carbon ions were simulated at different incident energies using the open source software GEANT4 version 10.3.2 via GATE v.8.0. The depth where the Bragg peaks of protons with incident energies of 75 MeV, 100 MeV, 130 MeV, 150 MeV, and 160 MeV in different materials were determined and the results were compared with the experimental data from the National Institute of Standards and Technology (NIST) database. The corresponding energy for incident carbon ion beam that yields the same Bragg peak position as the incident proton beams were also investigated. The depth-dose profile obtained using carbon ions show better dose conformation, but the presence of dose tail was observed. This suggests that further investigation of the RBE of the secondary fragments is necessary to understand their underlying impact to the carbon ion treatment in general.

Sputtering of nanostructured tungsten and comparison to modelling with TRI3DYN

He-induced nanostructured tungsten (so-called W-fuzz) was bombarded with Ar ions under 60° and the dynamic erosion behaviour was experimentally investigated. By using a highly sensitive quartz-crystal-microbalance technique in a particle catcher configuration, the sputtered particles distribution of W-fuzz could be evaluated. In contrast to a flat sample, where sputtered particles are emitted primarily in forward direction, we find that W-fuzz samples emit sputtered particles preferably in backward direction (i.e. in the direction of the incident ion beam). After continuous Ar irradiation of a W-fuzz sample the distribution approaches that of a flat sample. In addition to experimental data we also show modelling results obtained with a state-of-the-art Monte-Carlo (MC) binary collision approximation (BCA) code TRI3DYN in full 3D. Surface morphology changes as monitored by SEM as well as the dynamic sputtering behaviour can be well reproduced by the full 3D MC-BCA code.

A new experimental setup to measure absolute cross section for electron emis-sion from atoms, molecules or nanoparticles upon ion collisions

SynopsisA newly developed crossed beam experimental setup that utilizes a velocity map imaging technique to simultaneously measure both emission energy and angle of electrons ejected from atoms, molecules or nano-particles upon ion collision will be presented. The incident ion beam is produced at the GANIL facility with incident energies from a few keV to a few MeV and the target beam density is monitored by a quartz crystal microbalance allowing for estimating absolute single or double differential cross sections.

单晶硅柱面反射镜离子束倾斜入射加工工艺优化

单晶硅柱面反射镜离子束倾斜入射加工工艺优化

Ion bombardment induced formation of self-organized wafer-scale GaInP nanopillar assemblies

Ion sputtering assisted formation of nanopillars is demonstrated as a wafer-scale, lithography-free fabrication method to obtain high optical quality gallium indium phosphide (GaInP) nanopillars. Compared to binary materials, little has been reported on the formation of self-organized ternary nanostructures. Epitaxial (100) Ga0.51In0.49P layers lattice matched to GaAs were sputtered by nitrogen (N2) ions with relatively low ion beam energies (∼400 eV) to reduce ion bombardment induced damage. The influence of process parameters such as temperature, sputter duration, ion beam energy, and ion beam incidence angle on the pillar formation is investigated. The fabricated GaInP nanopillars have average diameters of ∼75–100 nm, height of ∼220 nm, and average density of ∼2–4 × 108 pillars/cm2. The authors show that the ion beam incidence angle plays an important role in pillar formation and can be used to tune the pillar shape, diameter, and spatial density. Specifically, tapered to near cylindrical pillar profiles together with a reduction in their average diameters are obtained by varying the ion beam incidence angle from 0° to 20°. A tentative model for the GaInP nanopillar formation is proposed based on transmission electron microscopy and chemical mapping analysis. μ-Photoluminescence and μ-Raman measurements indicate a high optical quality of the c-GaInP nanopillars.

3-D SRIM Simulation of Focused Ion Beam Sputtering with an Application-Oriented Incident Beam Model

Ion beam sputter etching has been widely used in material surface modification and transmission electron microscope (TEM) sample preparation. Due to the complexity of the ion beam etching process, the quantitative simulation of ion beam sputtering is necessary to guarantee precision in surface treatment and sculpting under different energies and beam currents. In this paper, an application-oriented incident ion beam model was first built with aberrations and Coulomb repulsion forces being considered from the Ga ion source to the sample. The sputtering process of this model on the sample was then analyzed and simulated with an improved stopping and range of ions in matter (SRIM) program. The sputtering performance of this model, the point-like incident beam and the typical Gaussian incident beam was given in the end. Results show that the penetration depth of Ga ions having 30 keV energy in silicon is 28 nm and the radial range is 29.6 nm with 50 pA beam current. The application-oriented model has been verified by our focused ion beam-scanning electron microscopy (FIB-SEM) milling experiment and it will be a potential thermal source in simulating the process of FIB bombarding organic samples.

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°.

The mechanism of negative and positive hydrogen ions production on the Ni surface

The studies about surface production of hydrogen negative ions play an important role in many technologies. In the present paper, a low energy molecular hydrogen ion beam was irradiated to the porous Ni sheet. It was found that negative atomic hydrogen ions were detected at the back of the porous Ni sheet when the energy of incident ion beam was lower than 180 eV. When the energy of the incident ions increased, the positive ions dominated at the back of the porous Ni sheet. The production of negative hydrogen on Ni surface can't be explained by comparing the electron affinity of Ni and H. The charge transferring during the process of H atoms reflected from Ni surface was calculated by using constrained DFT (cDFT). The results show the production of negative hydrogen on Ni surface may well be due to heterogeneous electron density on the Ni surface. However, the influence of incident energy on the production of negative and positive hydrogen ions is unable to be explained by cDFT. The problem may be solved by using TDDFT which is able to capture the transfer of energy to electrons during the collision between atoms.

Surface modified solution‐derived nickel oxide film via ion‐beam irradiation as a liquid crystal alignment layer

AbstractIn this article, we demonstrate the liquid crystal (LC) alignment characteristics of solution‐derived nickel oxide (NiO) film modified with ion‐beam (IB) irradiation. Cross‐polarized optical microscopy and pretilt angle measurements verified that uniform LC alignment was achieved using the NiO film as an alignment layer regardless of IB incidence angle. Contact angle measurements revealed that all of the NiO films had a deionized water contact angle below 90°, which indicates that they had hydrophilic surfaces that had an effect on the homogeneous LC alignment. Atomic force microscopy was conducted to determine the physical surface modification due to the IB irradiation, which showed that it reduced the size of the surface grains with agglomerations depending on the surface tilt from the IB incidence angle. Furthermore, microgroove structures strongly related to uniform LC alignment were observed after IB irradiation. Chemical surface modification was investigated via an X‐ray photoelectron spectroscopy analysis which revealed that IB irradiation modified the chemical bonds in the NiO film, and this affected the LC alignment state. Thus, these results indicate that using NiO film exposed to IB irradiation as an alignment layer is a suitable method for LC applications.

Bending of nanoporous thin films under ion radiation

In general, fundamental understanding of radiation resistance of high surface density nanoporous materials and nanoporous coatings is severely lacking. In this contribution ion-induced bending phenomena are studied in free-standing nanoporous Au cantilevers with thickness in the range of 100 to 200 nm. Experiments were performed in a Tescan Lyra dual beam system with Ga+ ion irradiation normal to the sample surface up to a maximum fluence of ~3 × 1019 m−2. Cantilevers bend towards the incident ion beam. It was found that the sensitivity of nanoporous Au samples to radiation-induced bending is substantially higher in comparison to the solid bulk counterparts. The process is described in terms of ion-induced coarsening of the structure top layers, which generates a volume contraction responsible for the bending moment. Therefore it is concluded that radiation-induced coarsening/sintering leads to negative swelling. Radiation-modified effective Young's modulus of the top layers was shown to influence essentially the fluence dependence of bending curvature. Model predictions agree well with our experimental findings showing that inhomogeneous radiation-induced coarsening of nanoporous structure results in bending and that nanoporous materials are less suitable for coatings in nuclear applications under the test conditions.

Physicochemical analysis of ion beam-induced surface modifications on polyethylene glycol films for liquid crystal alignment

ABSTRACTWe investigated the surface modification induced by the ion-beam (IB) irradiation of a polyethylene glycol (PEG) film and its liquid crystal (LC) alignment characteristics. The X-ray photoelectron spectroscopy analysis revealed the chemical modification; as the IB incidence angle increased, the number of surface C–O bonds decreased, inducing an anisotropic dipole moment on the PEG film surface. In addition, the physical modification was demonstrated via atomic force microscopy analysis using three-dimensional images as a function of the IB incidence angle. The surface roughness was analyzed; the modification with the smoothest surface was observed for an IB incidence angle of 45°. This modification affected the LC alignment state of the PEG film, as demonstrated by the polarized optical microscopy analysis with pre-tilt angle measurements. Furthermore, for the same IB incidence angle, the residual DC measured using the capacitance–voltage curves was extremely low. Hence, a PEG film irradiated with an IB incidence angle of 45° could be a suitable LC alignment layer.

Formation of the Temperature Field of Dielectric Films and of a Base in the Field of a Continuous Ion Beam

The influence of the temperature dependence of the thermal conductivity and heat transfer coefficients, as well as of the emissivity of a dielectric film and of an insulating base on formation of a stationary temperature field of the dielectric–base system exposed to irradiation by a continuous ion beam in air, has been studied theoretically. Analytical expressions have been obtained for the temperature fields of a sample and base, as well as a system of interrelated nonlinear algebraic equations for characteristic temperatures. With the aid of numerical solution of a system of nonlinear algebraic equations, the dependences of the temperature of the irradiated surface of the sample–base system and of the rear side of this system on the incident ion beam parameters have been found. It has been established that these dependences are nonlinear. It has been found that heating of a sample, including its irradiated surface, decreases substantially with increase in the thermal conductivity of the base.

Atomistic Simulations of the Efficiencies of Ge and Pt Ion Implantation into Graphene

Recent success in the direct implantation of 74Ge+ ion, the heaviest atomic impurity to date, into monolayer graphene presents a general question of the efficiency of low-energy ion implantation technique for heavy atoms. A comparative computational study, using classical molecular dynamics, of low-energy Ge and Pt ions implantation into single- and double-layer graphene is presented. It confirms that the highest probability for the perfect substitutional doping of single-layer graphene, i.e., direct implanting of ion into monovacancy, can be achieved 80 eV and it reaches the value of 64% for Ge ions directed at 45° angle to graphene plane and 21% for Pt ion beam perpendicular to graphene. Implantation efficiency is strongly dependent on the angle of ion beam. The sputtering yield of carbon atoms is found to be lower for double layer of graphene, which has better protective properties against low-energy ion irradiation damage than a single graphene layer. In double-layer graphene, incident ions traveling in the direction perpendicular to graphene can be trapped between the layers with the highest efficiency above or equal to 80% in the energy range of 40–90 eV for Ge ions and above 90% in the energy range of 40–70 eV for Pt ions. The energy range corresponding to the efficient trapping of ions in double-layer graphene is shifted toward higher energies upon tilting of the angle of incident ion beam.