Ion Beam Incidence Angle Research Articles

Study of the topography of silicon surface evolution under irradiation by a gallium ion beam

The silicon surface was irradiated with 30 keV gallium ion beam at incidence angles from 0 to 50° and fluences from 6·1016 to 5·1018 cm−2. Surface topography was investigated by scanning electron microscopy. It was found that one of four types of a relief can be formed on the silicon surface depending on the ion beam incidence angle and these fluences. Pattern formation starts with fluences of ∼2·1017 cm−2. The peculiarities of a relief evolution can be explained by the angular dependences of silicon sputtering with gallium ion beam and the possible existence of implanted gallium in the near-surface layer in the form of precipitates.

Ion beam figuring with focused anode layer thruster.

This work presents the peculiarities of cone ion beam formation with a focused thruster with anode layer (TAL) and its application to silicon carbide (SiC) ion beam figuring. Modeling results of Lorentz E × B force distribution in the discharge gap are presented. 3D particle tracing for keV Ar ions is carried out for the first time in the beam drift region of TAL with magnetic lens. Extracted ion beam full width at half maxima is about 2mm in the focal plane, where the SiC etching rate reaches 0.5 µm/min. The SiC sputter yields are measured as a function of the Ar ion impact energy and beam incidence angle. The maximum sputter yield of 2.8 atom/ion is observed at 45° of the beam-sample angle for the Si targets. Furthermore, the maximum sputter yield value of 1.7 atom/ion is measured at 30° of the beam-sample angle for the SiC targets. The novelty of present research is in the application of focused TAL keV Ar ion beam to the SiC ion beam figuring.

Liquid crystals alignment and switching between surface reinforced poly(ethylene-co-vinyl acetate) thin layers

The alignment characteristics of liquid crystals (LCs) on poly(ethylene-co-vinyl acetate) (PEVA) films via ion-beam (IB) irradiation at incidence angles of 15°, 45°, or 75° were investigated. Uniform and homogeneous LC alignment were achieved with a PEVA film IB-irradiated at an incidence angle of 45°. Physicochemical modification progressed by IB irradiation were examined by using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The AFM results show that the plasma argon ions penetrated and thereby increased the surface roughness and decreased kurtosis of the PEVA. The XPS results suggest that chemical reconstruction of the PEVA film induced the van der Waals forces and dipole-dipole interactions with the LCs. These transformations resulted in uniform LC alignment at 45° IB incident angle, as confirmed by polarized optical microscopy and pre-tilt angle measurements. The 45° incidence-angle IB-irradiated PEVA film also showed high transmittance in the visible light region. A twisted nematic LC cell based-on the PEVA film showed successful electro-optical performance as stable switching behavior and fine operation characteristics. These results indicate that IB irradiation is an effective method for uniform LC alignment and the 45° incidence-angle IB-irradiated PEVA film can be adopted for LC alignment in future LC display applications.

Tunable alignment of liquid crystals between anisotropic polyacrylamide thin layer

We report uniform liquid crystal (LC) alignment on a polyacrylamide (PAM) film via ion beam (IB) treatment. The IB incidence angle is adjusted from 15° to 75°. Physicochemical modifications caused by the IB process are investigated by atomic force microscopy and x-ray photoelectron spectroscopy. Low IB incidence results in biased and bumpy surfaces, whereas high IB incidence forms isotropic and smooth surfaces; both of these are unsuitable for uniform LC alignment. The 45° IB incidence induces anisotropic surface chemical reformations, and these modifications induce van der Waals forces between the LCs and modified PAM, thereby leading to uniform LC alignment. The LC alignment state is verified by polarized optical microscopy and pretilt angle. The electro-optical characteristic of the modified PAM showed excellent switching performance in twisted-nematic LC system. Thus, the IB-treated PAM film is a good candidate for LC alignment layers and suitable for LC device applications.

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.

Effect of focused ion beam process parameter on Tin-Nickel-Copper micropillars microfabrication

ABSTRACTIn this work, the mechanism of focused ion beam (FIB) milling as an advanced manufacturing technique is studied to pattern micropillars at different diameter sizes of 5, 10 and 20 μm. Under the same type of ion source which is Ga ion, the main ion beam parameters that influenced the FIB machining to produce micropillars are the ion beam scanning, dose, profile, and incident angle. The mathematical modeling is presented to describe the micropillars’ production by crater sputtering of the FIB milling. The effect of sputtering and redeposition on the final geometrical micropillars suggest the arrangement of the multilayer sample (Sn/Ni/Cu) that close to the ion irradiation gets highly sputtered and redeposited despite the surface binding energy and sputtering yield, ϒ of each element is known. Results show that the highest aspect ratio values are derived from the lowest diameter size of the micropillars produced from the FIB machining.

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.

Ion irradiation of III–V semiconductor surfaces: From self-assembled nanostructures to plasmonic crystals

Ion-irradiation of semiconductor surfaces has emerged as a promising approach to generate a variety of self-organized nanostructures. Furthermore, the combination of focused-ion-irradiation with molecular-beam epitaxy provides unprecedented design and control of surfaces and interfaces of hybrid materials at the atomic level during fabrication. In this review, we describe the directed self-assembly of nanostructure arrays ranging from islands to nanorods to 3-dimensional nanoparticle (NP) arrays. First, we discuss focused-ion-irradiation of III–V surfaces, which leads to preferential sputtering of group V species, followed by the formation of group III-rich metallic nanostructures. For continued irradiation beyond a threshold dose, the nanoparticle (NP) evolution is determined by the sputtering yield and the local ion beam angle of incidence, resulting in arrays of nanoparticles, nanorods, or nanoparticle chains. In addition to describing the formation of close-packed embedded Ga:GaAs nanocomposites using overgrowth of focused-ion-beam fabricated NP arrays, we discuss the surface plasmon resonances of NP arrays as well as the influence of both surface and buried NP arrays on the GaAs photoluminescence efficiency. Finally, we discuss the potential of “plasmonic crystals” for plasmon-enhanced optoelectronics.

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.

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.

Large current ion beam polishing and characterization of mechanically finished titanium alloy (Ti6Al4V) surface

Ti6Al4V samples with a surface roughness of about 0.2 μm were polished by a high fluence ion beam source, and influences of the ion current, energy and incident angle on the surface roughness of Ti6Al4V were studied. The as-polished surfaces were characterized by laser scanning confocal microscopy (LSCM), atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXRD) and X-ray photoelectron spectroscopy (XPS). The LSCM images revealed that the density of pits in the original surface decreased greatly after the ion polishing process. In addition, the surface roughness calculated from these images proved that the mean value reduced to 53 nm with an ion energy, current and incident angle of 600 eV, 130 mA and 75°, respectively. The smoothing effect was also confirmed by the power spectral density (PSD) functions calculated from the AFM data. GIXRD patterns indicated that the Ti6Al4V samples mainly contain the hexagonal close packed (HCP) α-Ti, no recognizable peaks corresponding to the body centered cubic (BCC) β-Ti were observed. Furthermore, after the ion beam polishing process, the phase of all the as-polished samples kept steady. The XPS results revealed that C, O, Ti, Al and V were present in both the original as well as the polished samples. In addition, due to the highly reactive characteristics of Ti, Al and V elements, a higher signal for oxygen can also be observed on the outermost surface of the ion beam polished samples. The polishing process of Ti6Al4V surface bombarded by Ar ion beam is also simulated by binary collision approximation (BCA) code SDTrimSP, the effects of ion beam energy and incident angle on the sputtering yield were investigated. The results showed that the sputtering yield of Ti, Al and V atoms increased almost linearly with the ion energy. However, as for the influence of ion incident angle, the sputtering yield first increased gradually from 0° and peaked at about 65°, then decreased rapidly because the incident angle is too large for Ar ion to penetrate into the surface of Ti6Al4V sample.

Emission Theory of Amorphous Material Sputtering: the Dependence of the Sputtering Coefficient on the Angle of Primary Ion Beam Incidence

The dependences of the sputtering coefficient on the types of accelerated ions, their energy, and the angle of incidence on a target are calculated. For Ar–Si, Хе–С, and H–W systems, acceptable coincidence between the calculated and experimental data is obtained. Two mechanisms for secondary-particle ejection from solids are established; they determine the dependences of the base sputtering coefficient for the base on the energy and the angle of primary ion incidence on the target.

Defect formation and modulation during patterning supported graphene sheets using focused ion beams

Focused ion beams (FIB) have been employed to applications from physical to life sciences because of their capabilities of machining features with nanoscale precision, making them a promising candidate for patterning graphene. Nevertheless, there are limited applications of patterning graphene using FIB due to ion-induced damages. In this work, we performed molecular dynamics simulations and Raman spectra mapping experiments to study defect formation in Cu-supported graphene sheets during gallium ion FIB processes. Our simulation results indicate that ion bombardment induced constrained scattering of carbon atoms and sputtered copper atoms, creating more defects in graphene than patterning on free-standing graphene. We propose two approaches to mitigate FIB-induced damages: (1) lowering ion beam energy; and (2) tilting ion beam incidence angles. The first approach can effectively suppress damages with ion energy down to 1 keV; however, this is not feasible for experiments. In the second approach, we demonstrated that tilting ion incident angles result in asymmetric damage distribution, which can be leveraged to pattern graphene/2D materials by utilizing the lightly-damaged side for device fabrication while discarding the heavily damaged side. The present study reveals the formation of FIB-induced damage on supported graphene, and proposes an approach to pattern graphene/2D materials using FIB.

Thermally stable poly(styrene-maleic anhydride) layer modified by ion-beam for liquid crystal orientation

We report uniform and homogeneous liquid crystal (LC) alignment using ion beam (IB)-irradiated poly(styrene-maleic anhydride) (SMA) films as an alignment layer when the IB incidence angle is controlled. The molecular polarity on the SMA surface increased with IB irradiation, especially at an incidence angle of 30°, resulting in strong van der Waals forces between the LC molecules and the surface. Atomic force microscopy and X-ray photoelectron spectroscopy were used to determine the LC alignment mechanism. Chemical structure analysis indicated that the orientation of LC molecules was due to van der Waals forces and selective breaking of C–C bonds by IB irradiation. The potential application of SMA substrates as alignment layers for display devices was further supported by their higher thermal stability (220 °C) compared with that of conventional rubbed SMA (160 °C) and rubbed polyimide (160 °C). Therefore, LC cells with IB-irradiated SMA are potential candidates for alternative alignment layers in LC applications.

Inducement of homogeneous liquid crystal alignment on surface-reformed polyurethane films via manipulation of ion-beam irradiation incidence angle

ABSTRACTWe investigated the induced uniform alignment of liquid crystals (LCs) on a polyurethane (PU) ion-beam (IB) irradiated at a certain incidence angle. Polarized optical microscopy (POM) and the crystal rotation method were used to evaluate the LC alignment state. On PU films IB-irradiated with incidence angles of 60° or less, the LC cells exhibit a clear and uniform alignment. At an incidence angle of 75°, light scattering was observed via POM, indicating the randomly aligned state of the LC cells. Moreover, the calculated pretilt angles for LC cells on IB-irradiated PU at incidence angles of 15°, 30°, 45°, and 60° were 0.05°, 0.05°, 0.20°, and 0.18°, respectively. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used to confirm the effect of varying the IB irradiation incidence angle. The PU surface irradiated by IB was modified differently as the incidence angle changed. IB irradiation at low incidence angles broke C–C, C–O/C–N, and N–C(O)–O bonds and caused C=O bond formation by the dissociation of the N–C(O)–O bonds. The van der Waals interactions between the PU and LC matched the LC molecular interactions and the anisotropic characteristics could be maintained, thereby achieving a stable homogeneous LC alignment.

Simulation of RBS spectra with known 3D sample surface roughness

The Rutherford Backscattering Spectrometry (RBS) is a technique for elemental depth profiling with a nanometer depth resolution. Possible surface roughness of analysed samples can deteriorate the RBS spectra and makes their interpretation more difficult and ambiguous. This work describes the simulation of RBS spectra which takes into account real 3D morphology of the sample surface obtained by AFM method. The RBS spectrum is calculated as a sum of the many particular spectra obtained for randomly chosen particle trajectories over sample 3D landscape. The spectra, simulated for different ion beam incidence angles, are compared to the experimental ones measured with 2.0MeV 4He+ ions. The main aim of this work is to obtain more definite information on how a particular surface morphology and measuring geometry affects the RBS spectra and derived elemental depth profiles. A reasonable agreement between the measured and simulated spectra was found and the results indicate that the AFM data on the sample surface can be used for the simulation of RBS spectra.

Self-organized microstructures induced by MeV ion beam on silicon surface

Micro patterning of self organized structure on silicon surface is induced by ion implantation of energetic (MeV) copper ions. This work reports for the first time the ability of using energetic ions for producing highly ordered ripples and dots of micro sizes. The experiments are realized at the Tandem ion beam accelerator (3 MV) at the IBA laboratory of the Atomic Energy Commission of Syria. Similarly to nano patterning formed by slow ions, the formation of micro patterned structures dots and ripples is observed to be depending on the angle of ion beam incidence, energy and ion fluence. The observation of such microstructures formation is limited to a range of ion energies (few MeV) at fluence higher than 1.75 × 1017 ion cm−2. The patterned surface layer is completely amorphousized by the ion implantation. Shadowing effect is observed in the formation of microripples and superstructures in the top of ripples. The superstructure develops new morphology that is not observed before. This morphology has butterfly shape with symmetry in its structure.

Ion Beam Patterning of High-Density STT-RAM Devices

Dependence on ion beam energy, ion species, and incidence angles is investigated to reduce sidewall re-deposition on the magnetic tunnel junction barrier. Experimental and simulated etch data, for a representative spin-torque transfer random access memory structure with 40 nm critical dimension and 150 nm pitch, indicated a reduction in the sidewall re-deposition when operating at: high angle, high voltage, and with Xe as the source gas. The Monte Carlo binary collision model simulations showed re-deposition thickness reduced by ~75% with Xe versus Ar at 1 kV beam energy and 30° incidence angle.

Physical simulation of the long-term dynamic action of a plasma beam on a space debris object

A methodology is developed for physical (laboratory) simulation of the long-term dynamic action of plasma beam high-energy ions on a space debris object with the aim of removing it to a lower orbit followed by its burning in the Earth's atmosphere. The methodology is based on the use of a criterion for the equivalence of two plasma beam exposure regimes (in the Earth’ ionosphere and in laboratory conditions) and an accelerated test procedure in what concerns space debris object material sputtering and space debris object erosion by a plasma beam in the Earth's ionosphere. The space debris coating material (blanket thermal insulation) sputtering yield and normal and tangential momentum transfer coefficients are determined experimentally as a function of the ion energy and the ion beam incidence angle.

Tailoring the Orientation and Periodicity of Wrinkles Using Ion-Beam Bombardment.

The present study demonstrates that surface reformation in polydimethylsiloxane can be controlled using ion-beam (IB) irradiation. This can be done by simply varying the IB incidence angle and requires no change in the energy source. By controlling the incidence angle of IB irradiation, we were able to continuously control the pattern of the wrinkle structure, that is, a randomly formed pattern or an anisotropic one. Moreover, the directional characteristics of the wrinkle pattern control the alignment of liquid crystal molecules. This control is a function of the incidence angle of the IB. These simple methods can provide considerable flexibility in the fabrication of wrinkle structures.