Ion Beam Erosion 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.

Harnessing ion beam erosion engineering for controlled self-assembly and tunable magnetic anisotropy in epitaxial films

The engineering of the surface morphology and the structure of the thin film is one of the essential technological assets for regulating the physical properties and functionalities of thin film-based devices. This study presents an easy and handy approach to tailor the surface structure of epitaxial thin films utilizing low-energy ion beam. Here, we investigate the evolution of the surface structure and magnetic anisotropy (MA) in epitaxial Fe/MgO (001) model systems subjected to multiple cycles of ion beam erosion (IBE) after thin film growth. The growth of Fe film occurs in the form of three–dimensional islands and exhibits intrinsic biaxial MA. Following a few cycles of IBE, an induced uniaxial magnetic anisotropy leads to a split in the hysteresis loop, and the film displays almost uniaxial magnetic switching behavior. More distinctly, we present a clear and conclusive evidence of (2 × 2) reconstruction of the Fe surface due to the atomic rearrangement by IBE. Furthermore, 57Fe isotope sensitive nuclear resonance scattering measurement provides insight into the depth-resolved magnetic information due to the modified surface topography. We also demonstrate that thermal annealing can reversibly tune the surface reconstruction and induced UMA. The feasibility of the IBE technique by adequately selecting IBE parameters for surface structure modification has been highlighted apart from conventional tailoring of the morphology for the tuning of UMA and introduces a new dimension to our understanding of self-assembled surface morphology evolution by IBE.

Enhanced magnetic anisotropy and its thermal stability in obliquely deposited Co-Film on the nanopatterned substrate

The deliberate manipulation of magnetic anisotropy through controlled adjustments to surface and interface morphology has become important due to its potential applications in spintronics and magnetic memory devices. In the present work, oblique angle deposition (OAD) at 65° to the surface normal on a rippled substrate, keeping nanopatterns on the SiO2 substrate perpendicular to the OAD projection, has been used to induce in-plane uniaxial magnetic anisotropy (UMA) and its thermal stability in cobalt (Co) thin film. Prior to film preparation, the patterned substrate of wavelength 68 ± 4 nm and amplitude 3.4 ± 0.2 nm was prepared separately using a low-energy ion beam erosion (IBE) process. Grazing incidence small-angle X-ray scattering (GISAXS) and magneto-optical Kerr effect (MOKE) techniques have been used for film characterization. While GISAXS provided information about film structure and morphology, MOKE provided information about magnetic properties, thus making it possible to correlate the temperature-dependent evolution of morphology with that of UMA in the film. A clear anisotropy in the growth of Co film is found to result in strong UMA. Unlike previous studies, which typically observe a reduction in UMA strength with thermal annealing, the present work demonstrates a 31 % increase in UMA strength after annealing up to 200 °C, underscoring the importance of oblique angle deposition on nano-rippled substrates for achieving high UMA and ensuring its thermal stability up to moderate temperatures. The appearance of large UMA and its unusual temperature dependence is understood in terms of the shadowing effects and column coalescence, resulting in more robust shape anisotropy. This work provides insights into morphological anisotropy, elucidating the interplay of shadowing effects, shape anisotropy, and dipolar interactions within interacting column and ripple structures. This method gives rise to morphology-induced anisotropy, which can also be applied to other ferromagnetic films to enhance the magnetic anisotropy and ensure thermal stability.

Effect of Deformation Nanostructuring on the Ion-Beam Erosion of Copper

Effect of Deformation Nanostructuring on the Ion-Beam Erosion of Copper

Effect of deformation nanostructuring on ion-beam erosion of copper

The effect of deformation nanostructuring on ion-beam erosion of copper at high fluences of irradiation with 30 keV argon ions was experimentally studied. Deformation nanostructuring by high-pressure torsion was used to form an ultrafine grained structure with a grain size of ~0.4 µm in copper samples with an initial grain size about 2 µm. It was found that when a layer of thickness comparable to the grain size was sputtered, a steady-state cone-shaped relief was formed on the copper surface, the appearance of which did not change with increasing irradiation fluence. It has been shown that the smaller the grain size in copper, the greater the concentration and the smaller the cone height on the surface. The cone inclination angles, close to 82°, as well as the sputtering yield of 9.6 at./ion, practically does not depend on the copper grain size, the thickness of the sputtered layer, and the irradiation fluence. Calculations using the SRIM code showed that when taking into account the sputtering of atoms from the walls of the cones, the sputtering yield of a cone-shaped copper relief Үc, was 3.5 times less than the yield of a single cone, 1.2 times greater than the sputtering yield of a smooth surface, and the value of 9.25 at./ion was close to the experimentally measured one.

Low-energy ion beam erosion of Si with simultaneous co-deposition of metallic surfactants: Experimental and simulated data

Ion beam erosion of Si under co-deposition circumstances supports the formation of surface patterns on the nano- and micrometer scale. To evaluate the effect of surfactant sputtering within a setup relevant for ultra precision surface finishing, this work is presented. We present data for samples prepared with Ar ion beam erosion, at low ion energy. Al, Cu, steel, Cr, Ni, Mo, Ti, Ta, Zn and Si were chosen as co-deposition material. Simultaneous irradiation of the co-deposition material and the Si samples were performed with a broad beam ion source. The structuring and pattern formation are discussed with SEM and AFM measurements. It was shown that the evolution of structures on the substrate is induced by the silicide-forming metals. This corresponds with a higher surface roughness. Whereas the non-silicide-forming metals did not show patterning, and accordingly, lower surface roughness. Measurements regarding the Si removal rate showed, that it depends on the co-deposition material. Supporting simulation data proposed that the effect of the co-deposition material on the Si removal is determined by the combination of sputtering and scattering properties of the co-deposition material. The ratio of scattered Ar ions to sputtered metal particles describes the effect on the removal change. For metals which tend to higher scattering, the removal is enhanced. This applies for most of the metals with higher atomic number. Whereas the metals with lower atomic number favor self-sputtering, which results in an decreased Si removal.

The Erosion of selected tungsten coatings by ion beam and plasma sources compared to calculated predictions

Tungsten is proposed as a tokamak divertor armour due to its good erosion resistance. Combining tungsten coatings with copper as a base material can overcome problems with machinability, lower the weight and reduce the component cost. The erosion rate must be known to estimate the lifetime of plasma facing components.This work aims to compare selected tungsten coatings to check if the erosion rate remains as good. It also compares the experimental data to a developed code based on previous work that aims to be quick and simple while giving reasonable results.In this study a set of erosion experiments were undertaken to measure the sputter yield in different conditions at partner organisations; Helium ion beam erosion at Huddersfield University, Helium plasma erosion at the University of Liverpool, Argon plasma erosion at Plasma Quest Ltd and Xenon Focussed Ion Beam (FIB) erosion at University of SurreyThis work compares sputter yields different tungsten samples: sheet material, Chemical Vapour Deposition tungsten coating, Additive Manufacture deposited tungsten and tungsten coatings laid down by Thermal Plasma Spray. These coatings are available commercially so are ready to deploy today.The experimental sputter yields were compared to theoretical predictions, based on previously published work. While the experimental results agreed well with the models in trend and angular dependence the quantitative agreement was only well predicted to within a factor of four.It was found that the coatings have similar, and sometimes slightly lower sputter yields, and therefore, on occasion, slightly better erosion performance than the stock tungsten sheet samples.

Enhancing the limit of uniaxial magnetic anisotropy induced by ion beam erosion

Artificial tailoring of magnetic anisotropy by manipulating interfacial morphology and film structure is of fundamental interest from an application point of view in spintronic and magnetic memory devices. This Letter reports an approach to engineer and enhance the strength of oblique incidence ion beam erosion (IBE)-induced in-plane uniaxial magnetic anisotropy (UMA) by simultaneous modification of film morphology and film texture. Cobalt film and Si substrate have been taken as a model system to meet this objective. Unlike conventional thin film deposition on ripple patterned substrate or post-growth IBE of film, we direct our effort to the sequential deposition and subsequent IBE of the film. Detailed in situ investigation shows that the film grows in a textured polycrystalline state with the formation of nanometric surface ripples. The film also exhibits pronounced UMA with an easy axis oriented parallel to the surface ripple direction. Remarkably, the induced UMA is about one order of magnitude larger than the IBE-induced UMA reported earlier. The capability of imposing in-plane crystallographic texture throughout the film layer gives rise to magneto-crystalline anisotropy along with the shape anisotropy of nanometric surface ripples, which enhances the strength of the UMA and illustrates the universal applicability of the present method.

Ripple pattern formation on silicon carbide surfaces by low-energy ion-beam erosion

A versatile experimental facility air insulated high current medium energy 200 kV Ion Accelerator, with the terminal voltage in the range of 30-200 kV has been running successfully at Ion Beam Centre, KUK for carry out multifarious experiments in material science and surface physics. This system offers single charge state, switching magnet with five exit ports and large area irradiation/implantation using hollow cathode ion source. Ion beam induced structures on the surfaces of semiconductors have potential applications in photonics, magnetic devices, photovoltaics, and surface-wetting tailoring etc. In this regard, silicon carbide (SiC) is a fascinating wide-band gap semiconductor for high-temperature, high-power and high-frequency applications. In this work, fabrication of ripple patterns is carried out on the SiC surfaces using 80 keV Ar+ ion beam for different fluences at oblique incidence of 500. AFM study demonstrates that ripple wavelength and amplitude, ordering and homogeneity of these patterns vary linearly with argon ion fluence. The formation of such surface structures is attributed to the preferential sputtering of silicon in comparison to carbon. The evolution of high degrees of order is explained with the help of existing formalisms of coupling between surface topography and preferential sputtering.

Morphology induced large magnetic anisotropy in obliquely grown nanostructured thin film on nanopatterned substrate

The artificial tailoring of magnetic anisotropy by manipulating surface and interface morphology is attracting widespread interest for its application in spintronic and magnetic memory devices. Here oblique angle deposition on a nanopatterned rippled substrate is presented as a novel route of inducing large in-plane uniaxial magnetic anisotropy (UMA) in magnetic thin films. For this purpose, Cobalt films and rippled SiO2 substrates have been taken as a model system for the present study. Here, nanopatterned substrates are prepared by low energy ion beam erosion (IBE), above which films are deposited obliquely along and normal to the ripple directions. A clear anisotropy in the growth behavior has been observed due to the inhomogeneous in-plane organization of adatoms in the form of columns. The increased shadowing effect in the films deposited obliquely normal to the direction of the ripple patterns causes preferential coalescence of the columns along the substrate ripples, resulting in stronger in-plane UMA in the film. This peculiarity in magnetic behavior is addressed by considering the morphological anisotropy governed by enhanced shadowing effect, the shape anisotropy and the dipolar interactions among the magnetostatically coupled ripple structure.

Evolution of a notched surface under glancing-angle broad ion beam erosion

Recently, a novel approach to sample preparation for microstructure analyses has been introduced where a surface possessing initial notches is eroded by a broad ion beam at gracing angles. In this contribution, details of the evolution of the sample surface and the geometry obtained are investigated in depth, using both simulation and experiments on single-crystalline Si substrates. A framework is introduced which describes the surface by a linear model and allows easy application for given sample preparation tasks. Furthermore, the surface amorphization introduced during sample preparation is evaluated using cross-sectional high-resolution transmission electron microscopy.

Ion incidence angle dependent pattern formation at AZ 4562® photo resist by Ar+ ion beam erosion

Interactions between ion beams and polymers have great potential to tailor the properties of the polymer surface by modifying the morphology as well as the chemical composition. The application of a wide range of ion incidence angles (0° - 75°) for the erosion of the commercially available photoresist AZ 4562® revealed a multitude of nanopatterns as investigations using atomic force microscopy and scanning electron microscopy have shown. A sequence of angle-dependent patterns (nanoholes, ripples, facets) can be observed, which are already known from inorganic materials. Additionally, the variation of the erosion time (5 min – 60 min) showed an evolution of the nanopatterns. A changed composition of the polymer surface could be detected by means of X-ray photoelectron spectroscopy.

In-Situ Investigation of Ion Beam-Induced Crossover in Uniaxial Magnetic Anisotropy of Polycrystalline Fe Films

A combined role of structure and morphology of polycrystalline Fe thin films in the evolution of uniaxial magnetic anisotropy (UMA) subjected to several cycles of the ion beam erosion (IBE) process...

Tailoring of uniaxial magnetic anisotropy in Permalloy thin films using nanorippled Si substrates

In this work the investigation of in-plane uniaxial magnetic anisotropy induced by the morphology due to ion beam erosion of Si(1 0 0) has been done. Ion beam erosion at an oblique angle of incidence generates a well-ordered nanoripple structure on the Si surface and ripple propagates in a direction normal to ion beam erosion. Permalloy thin films grown on such periodic nanopatterns show a strong uniaxial magnetic anisotropy with easy axis of magnetization in a direction normal to the ripple wave vector. The strength of uniaxial magnetic anisotropy is found to be high for the low value of ripple wavelength; it is decreasing with increasing value of ripple wavelength. Similarly, the strength of uniaxial magnetic anisotropy decreases with increasing Permalloy film thickness. Grazing incidence small angle x-ray scattering data reveals an anisotropic growth of Permalloy thin films with preferential orientation of grains in the direction normal to the ripple wave vector. Permalloy thin film growth is highly conformal with the film surface replicating the substrate ripple morphology up to a film thickness of 50 nm has been observed. Correlation between observed uniaxial magnetic anisotropy to surface modification has been addressed.

Modelling of Optical Damage in Nanorippled ZnO Produced by Ion Irradiation

Here, we report on the production of nanoripples on the surface of ZnO bulk substrates by ion beam erosion with 20 keV Ar+ ions at an oblique incidence (60°). The ripple patterns, analyzed by atomic force microscopy, follow a power law dependence for both the roughness and the wavelength. At high fluences these ripples show coarsening and asymmetric shapes, which become independent of the beam direction and evidence additional mechanisms for the pattern development. The shallow damaged layer is not fully amorphized by this process, as confirmed by medium energy ion scattering. A detailed study of the damage-induced changes on the optical properties was carried out by means of spectroscopic ellipsometry. Using a 3-layer model based on Tauc-Lorenz and critical point parameter band oscillators, the optical constants of the damaged layer were determined. The results showed a progressive reduction in the refractive index and enhanced absorption below the bandgap with the fluence.

Dynamic scaling behavior of mica ripples produced by low energy Ar+ ion erosion

The scaling behavior of ion beam induced ripple patterns on mica surface is investigated by means of atomic force microscopy (AFM). The ripples were produced by 12 keV Ar+ ion beam erosion at an angle 60° with respect to the surface normal. Ripple wave-vectors are found to align parallel to the ion beam projection direction. The root-mean-square (rms) roughness and lateral correlation length of the rippled surface are observed to increase with ion fluence with a growth exponent β = 0.51 ± 0.04 and dynamic exponent 1/zx = 0.42 ± 0.07 along the ripple direction as well as 1/zy = 0.34 ± 0.09 normal to the ripple direction respectively. Ripple wavelength is also found to increase slowly with ion fluence upto ϕ ∼ 6 × 1017 ions.cm−2 and then shows a rapid coarsening behavior with an exponent n = 0.43 ± 0.04. The two different roughness exponents, αx and αy, along and normal to the ripple direction, are also calculated from their corresponding power spectral density function and found the values 1.25 ± 0.09 and 1.20 ± 0.08 respectively. The scaling properties of ripple growth for long time ion bombardment and the overall morphological changes are explored according to calculated erosive and redistribution coefficients in the framework of recently advanced continuum models of pattern formation by ion beam sputtering. The production of ripples is found to be driven by mass-redistribution effects rather than curvature dependent sputter erosion. This is an worth addition to the understanding of ion beam nanopatterning process as it ascertains mass redistribution as indispensable phenomena for pattern formation not only for ion energies less than 1 keV but also for ion irradiation of energy range 10 keV and above.

Rapid and localized ion-beam etching of surfaces using initial notches

Glancing-angle Ar+ broad ion beam erosion is widely used for the preparation of high-quality transmission electron microscopy (TEM) samples. However, low erosion rates and lack of site specificity are major drawbacks of the method. Being inexpensive and easy to use – in particular when compared to widely used focused ion beam preparation methods – overcoming these drawbacks would significantly improve many existing preparation workflows. We present a novel method for rapid and localized surface erosion which combines laser-machining preprocessing with broad ion beam etching. In this article, preliminary studies of the method on bulk samples are reported. Furthermore, an electron-transparent lamella has been prepared as proof of concept.Using an ultrashort-pulsed solid-state laser, notches were created on (100)-Si substrates. Due to the local change in surface inclination, preferential erosion took place behind the notches upon subsequent ion beam etching at glancing angles. As a consequence, a terrace structure possessing a well-defined jump in surface height was formed. The surface topography and its evolution dynamics were characterized and the findings compared to numerical simulations based on a deterministic, two-dimensional model. On this basis, a workflow utilizing these initial notches (iNotches™) for the preparation of an electron transparent lamella was realized and TEM micrographs of the prepared sample were taken.

Study of pattern transition in nanopatterned Si(100) produced by impurity-assisted low-energy ion-beam erosion

In this work, formation of self-organized Si nanostructures induced by pure Fe incorporation during normal incidence low-energy (1keV) Ar $$^+$$ ion bombardment is presented. It has been observed that the incorporation of Fe affects the evolution of the surface topography. The addition of Fe generates pronounced nanopatterns, such as dots, ripples and combinations of dots and ripples. The orientation of the ripple wave vector of the patterns formed is found to be in a direction normal to the Fe flow. The nanoripples with wavelength of the order of 39 nm produced is expected to be the lowest wavelength of the patterns reported on ion-beam-eroded structures under the incorporation of metallic impurities as per our knowledge. From the AFM and GISAXS analysis, it has been confirmed that the ripples formed are asymmetric in nature. The effect of the concentration of the Fe on morphological transition of the patterns has been studied using Rutherford backscattering measurements.

Continuum modeling of particle redeposition during ion-beam erosion

We thoroughly investigate the impact of redeposition on the self-organized pattern formation during ion-beam erosion within the framework of a spatially two-dimensional continuum model. An analysis on prestructured patterns allows the extraction of general properties of this mechanism, the typical distribution of redepositing particles and approximations in terms of the surface height in particular. By combining the redeposition model with erosion models, we present detailed results about the impact of redeposition on spatio-temporal surface evolutions. It is shown that redeposition can play a decisive role for pattern formation under ion-beam erosion within an extended range in the parameter space.

Investigation of the mechanism of impurity assisted nanoripple formation on Si induced by low energy ion beam erosion

A detailed mechanism of the nanoripple pattern formation on Si substrates generated by the simultaneous incorporation of pure Fe impurities at low energy (1 keV) ion beam erosion has been studied. To understand and clarify the mechanism of the pattern formation, a comparative analysis of the samples prepared for various ion fluence values using two complimentary methods for nanostructure analysis, atomic force microscopy, and grazing incidence small angle x-ray scattering has been done. We observed that phase separation of the metal silicide formed during the erosion does not precede the ripple formation. It rather concurrently develops along with the ripple structure. Our work is able to differentiate among various models existing in the literature and provides an insight into the mechanism of pattern formation under ion beam erosion with impurity incorporation.