Oblique Ion Research Articles

Smoothing of polycrystalline copper with rough surface by oblique argon-ion irradiation

Mechanically polished polycrystalline copper was obliquely irradiated by an argon-ion beam with an ion energy of 1keV. The incident angle and fluence of the argon ion were changed to obtain the dependences of incident angle and ion fluence on the surface flatness. After argon-ion irradiation, the surface flatness was examined using atomic force microscopy. Before the irradiation, the sample had a rough surface consisting of groove structures with an average width of 400nm and an average elevation of 37nm. The percentage of the surface area with a height more than 50nm was 13%. The incident angle was changed from 0° (perpendicular injection) to 70° for the fluence of 1×1018Ar∕cm2. The fluence was changed in the range of 1×1017–1×1018Ar∕cm2 for the incident angle of 70°. A smooth surface was obtained when the incident angle was largest, 70°, and the fluence was greater than 5×1017Ar∕cm2. The percentage of the surface area with an elevation more than 50nm was reduced to 2%, and the number of grooves per unit area was reduced to about half. The reduction of the elevation is mainly due to the selective sputtering for protruding parts, and the reduction of the groove number is mainly due to the redepositing of sputtered particles. The present results show that the oblique ion irradiation is useful for reducing both the elevation and the number of grooves of uneven surfaces.

Ion-induced self-organized dot and ripple patterns on Si surfaces

The evolution of the surface topography during low-energy Ar + ion beam erosion of silicon surfaces is studied. Depending on ion-beam parameters, a variety of nanostructured patterns with a very narrow size distribution can be developed on the surface. By rotating the sample, ordered nanodots are formed for ion energies ⩾300 eV at normal and oblique ion incidence angles with respect to the surface normal. Dots evolving at oblique ion incidence of 75° show a very high degree of ordering with a mean dot size λ∼30 nm. Without sample rotation at near normal ion incidence angle (∼15°), remarkably ordered ripple structures develop with a wavelength λ∼45 nm. The degree of ordering and size homogeneity of these nanostructures increases with erosion time eventually leading to the most ordered self-organized patterns on Si surfaces reported so far.

Generation of filamentary structures by beam-plasma interaction

The previous simulations by Wang and Lin [Phys. Plasmas. 10, 3528, (2003)] showed that filaments, frequently observed in space plasmas, can form via the interaction between an ion beam and a background plasma. In this study, the physical mechanism for the generation of the filaments is investigated by a two-dimensional hybrid simulation, in which a field-aligned ion beam with relative beam density nb=0.1 and beam velocity Vb=10VA is initiated in a uniform plasma. Right-hand nonresonant ion beam modes, consistent with the linear theory, are found to be dominant in the linear stage of the beam-plasma interaction. In the later nonlinear stage, the nonresonant modes decay and the resonant modes grow through a nonlinear wave coupling. The interaction among the resonant modes leads to the formation of filamentary structures, which are the field-aligned structures (k⊥B) of magnetic field B, density, and temperature in the final stage. The filaments are nonlinearly generated in a prey-predator fashion by the parallel and oblique resonant ion beam modes, which meanwhile evolve into two types of shear Alfvén modes, with one mainly propagating along the background field B0 and the other obliquely propagating. The filamentary structures are found to be phase standing in the plasma frame, but their amplitude oscillates with time. In the dominant filament mode, fluctuations in the background ion density, background ion temperature, and beam density are in phase with the fluctuations in B, whereas the significantly enhanced beam temperature is antiphase with B. It is found that the filaments are produced by the interaction of at least two ion beam modes with comparable amplitudes, not by only one single mode, thus their generation mechanism is different from other mechanisms such as the stimulated excitation by the decay of an Alfvén wave.

Self-organized dot patterns on Si surfaces during noble gas ion beam erosion

The erosion of target materials with energetic ions can lead to the formation of patterns on the surface. During low-energy (⩽2000 eV) noble gas (Ne +, Ar +, Kr +, Xe +) ion beam erosion of silicon surfaces dot patterns evolve on the surface. Dot structures form at oblique ion incidence of 75° with respect to surface normal, with simultaneous sample rotation, at room temperature. The lateral ordering of dots increases while the dot size remains constant with ion fluence, leading to very well ordered dot patterns for prolonged sputtering. Depending on ion beam parameters, dot nanostructures have a mean size from 25 nm up to 50 nm, and a mean height up to 15 nm. The formation of dot patterns depends on the ion/target mass ratio and on the ion energy. The temporal evolution and the lateral ordering of these nanostructures is studied using scanning force microscopy (AFM).

Interferometric identification of ion acoustic broadband waves in the auroral region: CLUSTER observations

We determine the phase velocity and k vector for parallel and oblique broadband extremely low frequency, ELF, waves on nightside auroral magnetic field lines at altitudes around 4.6 RE. We use internal burst mode data from the EFW electric field and wave instrument onboard the Cluster spacecraft to retrieve phase differences between the four probes of the instrument. The retrieved characteristic phase velocity is of the order of the ion acoustic speed and larger than the thermal velocity of the protons. The typical wavelength obtained from interferometry is around the proton gyro radius and always larger than the Debye length. We find that in regions with essentially no suprathermal electrons above a few tens of eV the observed broadband waves above the proton gyro frequency are consistent with upgoing ion acoustic and oblique ion acoustic waves.

Dynamical behavior of U-shaped double layers: cavity formation and filamentary structures

Abstract. Observations from the Polar and FAST satellites have revealed a host of intriguing features of the auroral accelerations processes in the upward current region (UCR). These features include: (i) large-amplitude parallel ( ) and perpendicular () fluctuating as well as quasi-static electric fields in density cavities, (ii) fairly large-amplitude unipolar parallel electric fields like in a strong double layer (DL), (iii) variety of wave modes, (iv) counter-streaming of upward going ion beams and downward accelerated electrons, (v) horizontally corrugated bottom region of the potential structures (PS), in which electron and ion accelerations occur, (vi) filamentary ion beams in the corrugated PS, and (vii) both upward and downward moving narrow regions of parallel electric fields, inferred from the frequency drifts of the auroral kilometric radiations. Numerical simulations of U-shaped potential structures reveal that such observed features of the UCR are integral parts of dynamically evolving auroral U-shaped potential structures. Using a 2.5-D particle-in-cell (PIC) code we simulate a U-shaped broad potentialstructure (USBPS). The dynamical behavior revealed by the simulation includes: (i) recurring redistribution of the parallel potential drop (PPD) in the PS, (ii) its up and downward motion, (iii) formation of filaments in the potential and density structures, and (iv) creation of filamentary as well as broad extended density cavities. The formation of the filamentary structures is initiated by an ion-beam driven instability of an oblique ion mode trapped inside a broad cavity, when it becomes sufficiently thin in height. The filaments of the PS create filamentary electron beams, which generate waves at frequencies above the lower hybrid frequency, affecting plasma heating. This results in plasma evacuation and formation of a cavity extended in height. The waves associated with filamentary electron beams also evolve into electron holes. The transverse and parallel scale lengths of the regions with large and as well as their magnitudes are compared with satellite data.

A Study on Electro-Optical Characteristics of the Ion Beam Aligned Fringe-Field Switching (FFS) Cell on the Inorganic Thin Film

ABSTRACT In this study, we investigated the electro-optical (EO) characteristic of fringe-field switching (FFS) mode cell by the ion beam alignment method on the a-C:H thin film. The suitable inorganic thin films for FFS cell and the aligning capabilities of nematic liquid crystal (NLC) using the new alignment material of a-C:H thin film were studied. An excellent voltage-transmittance (V-T) and response time curve of the ion beam aligned FFS cell was observed with oblique ion beam exposure on the a-C:H thin films. Also, the V-T hysteresis characteristics of the ion beam-aligned FFS cell with IB exposure on the a-C:H thin films is almost the same as that of the rubbing-aligned FFS cell on a polyimide (PI) surface.

Electro-Optical Characteristics of Photoaligned TN Cell Using UV Alignment on the a-C:H Thin Film

ABSTRACT We studied the nematic liquid crystal (NLC) alignment capability by the UV alignment method on a a-C:H thin-film surface, and investigated electro-optical performances of the UV aligned twisted nematic (TN)- liquid crystal display (LCD) with the UV exposure on a-C:H thin film surface. A good LC alignment by UV irradiation on a a-C:H thin-film surface at a layer thickness of 200 Å was achieved. Also, a good LC alignment by the UV alignment method on the a-C:H thin film surface was observed at an annealing temperature of 180°C. However, the alignment defect of the NLC was observed at an annealing temperature above 200°C. Monodomain alignment of the UV aligned TN-LCD can be observed. The best electro-optical (EO) characteristics of the UV aligned TN-LCD in the photoaligned TN-LCDs was observed with oblique ion beam exposure on the a-C:H thin film surface for 1 min.

Fractal analysis of roughness profile induced by ion bombardment of metal surface

Surface roughness, which plays or could play an important role in microelectronics, surface analysis, medicine and other branches of science and technology, is one of the more important aspects of ion bombardment-induced modification of surface morphology of solids. The results of profilometric and microscopic experiments showed dependence of measured surface roughness parameters upon the length of elementary segment (profilograph) or scanning area (AFM). The “scaling effects” are interesting and may be important in fractal analysis of ion sputtered surface. The paper presents an analysis in question relative to stainless-steel surface roughness profile generated by very oblique broad argon ion beam irradiation. The preliminary results obtained for normal bombardment and presented elsewhere have shown that fractal analysis, surface roughness measurement and surface topography observations may form a proper investigative tool which could give a relatively full picture of surface morphology modification during ion beam bombardment. Here, we tried to verify this conclusion for grazing incidence.

Liquid Crystal Alignment Effects and Electro Optical Performances of Twisted Nematic-Liquid Crystal Display Using Ion-Beam Alignment Method on Nitrogen-doped Diamond Like Carbon Thin Film Layer

Nitrogen-doped diamond-like carbon (NDLC) thin films exhibit a high electrical resistivity that is similar to the properties shown by diamond-like carbon (DLC) thin films. The diamond-like transport property in NDLC thin films comes from a material consisting of sp2-bonded carbon versus the sp3-bonded carbon of DLC. In addition, NDLC thin films have a better thermal stability than the DLC thin films, because C:N bonding in the NDLC thin films is stronger against thermal stress than C:H bonding in the DLC thin films. The liquid crystal (LC) alignment effects of ion beam irradiation on the NDLC thin films and the electro optical (EO) performances of the ion-beam-aligned twisted nematic (TN)-liquid crystal display (LCD) with oblique ion beam exposure on an NDLC thin film surface were studied. A good uniform nematic liquid crystal (NLC) alignment with ion beam exposure on the NDLC thin films was observed. In addition, good EO properties, a residual DC property and particularly the good thermal stability of the ion-beam-aligned TN-LCD on NDLC thin films was achieved.

Nanoscale periodic and faceted structures formation on Si(1 0 0) by oblique angle oxygen ion sputtering

The dynamics of ripple topography on silicon surfaces generated by oxygen ion bombardment with increasing fluences have been investigated by atomic force microscopy (AFM). At the early stages of sputtering, periodic ripples with the wave vector parallel to ion beam direction are developed. At the late stages of sputtering, the ripple structure tends to break down and the surface becomes faceted. The growth rate of the ripples and the scaling exponents of the faceted surface have been determined. The results are discussed with reference to the Bradley–Harper theory and its nonlinear extension. Finally, the ripple wavelength is found to be a linear function of the bombarding energy.

P-123: Electro-Optical Characteristics of the Ion-Beam-Aligned FFS Mode on the New a-C:H Thin Film

In this paper, we intend to make FFS (Fringe-Field Switching) mode cell with LC alignment by using non-rubbing method, ion beam(IB) alignment method on the new a-C:H thin film, to analyze electro-optical characteristics in this cell. We studied on the suitable inorganic thin film for FFS-LCD and the aligning capabilities of nematic liquid crystal (NLC) by using the new alignment material of the a-C:H thin film as working gas at rf bias condition. A high pretilt angle of about 5° by IB exposure on the new a-C:H thin film was measured. An excellent voltage-transmittance (V-T) and response time curve of the IB-aligned FFS-LCD were observed with oblique ion beam exposure on the new a-C:H thin films.

Effect of anomalous ion inertia and oblique ion viscosity on the radial electric field in FT-2 tokamak experiments

Results are presented from numerical simulations that show that, in a plasma with well-developed turbulence, the radial electric field can be positive in the region where the gradients of the plasma parameters are steep. In a plasma in which the turbulence is suppressed (as is the case with auxiliary lower hybrid heating), the radial electric field is found to exhibit a nearly neoclassical behavior during the formation of a transport barrier and transition to the H-mode.

Etching of polycrystalline copper by oblique injection of argon ion

In order to miniaturize large scaled IC (LSI) and/or produce a multi-layered LSI device, copper wire with a smooth surface is required. For reduction of the surface roughness, ion etching with oblique injection was applied for polycrystalline copper. Argon ion irradiation was conducted by changing the incident angle and ion energy. After irradiation, many blisters of various sizes were observed. During normal ion injection, the etched amount of copper increased with ion energy and the average height of blisters also increased. Then, blister formation can be adjusted by ion energy. As the incident angle increased, the blister size became smaller and the surface became smooth compared with normal ion injection. This result suggests that preferential sputtering occurred for the protuberant parts of blisters. In particular, when the incident angle is 67.5°, the average height of blisters became half of the normal value. The present result shows that oblique ion irradiation contributes to the reduction of surface roughness.

Electrical properties of superfilled sub-micrometer silver metallizations

Electrical properties of damascene silver wires with widths between ≈60 and 840 nm and heights between ≈100 nm and 300 nm are presented. The superconformal electrodeposition process by which the seam-free and void-free metallizations were fabricated is summarized. The chemical-mechanical polishing plus oblique ion sputtering process by which metal overburden was removed from the field adjacent to the wires is detailed. The size-dependent resistivity of the wires is obtained and interpreted in terms of intrinsic resistivity, grain boundary reflection, and surface scattering. Quantitative analysis of the last is accomplished using a different implementation of the Fuchs-Sondheimer formalism for wires of rectangular geometry and nonzero surface specularity that is derived herein.

Sub-micron structuring at mesa edges

A simple process for forming sub-micron gaps between horizontal and vertical electrodes in a three-dimensional micro-electrode system without the need for high-resolution lithography is described. The process is based on the enhancement of ion milling rates in metals at oblique ion incidence, which allows the preferential erosion of metal at a mesa edge. Self-aligned electrode structures are formed on silica and oxidised silicon mesas, and electrode separations of 150–300 nm are demonstrated in geometries that may be suitable for vertical knife-edge field emission sources.

LP‐8: Late News Poster: Ion Beam Sputter Deposition Process of Inorganic Vertical Alignment Layers

AbstractThe research results of silicon dioxide thin films alignment properties is presented. The films was deposited by oblique ion beam sputtering on glass substrate. Films thickness and angle condensation influences on the value of pretilt angle of liquid crystal vertical alignment mode is shown. Role of the surface morphology of alignment layers is discussed. The highly uniform vertical alignment layers can be produced using ion beam coating on the substrates with dimensions 300 × 400mm and more.

Room-temperature growth of a carbon nanofiber on the tip of conical carbon protrusions

Glassy carbon was Ar+-ion bombarded with a simultaneous Mo supply under ultrahigh vacuum conditions using a microprotrusion fabrication system that consists of a differentially pumped ion gun and a seed-material supply source. Conical protrusions were formed by sputtering with a seed supply, and carbon nanofibers (CNFs) grew on the tips even at room temperature. The length of CNFs reached up to ∼10 μm, and their diameter was almost uniform (50 nm) in the growth direction. The short CNFs aligned in the ion beam direction, whereas the long ones were non-aligned. The CNF growth on a glassy carbon surface was ascribed to the enhanced surface texturing and to the massive redeposition of C atoms onto cones, both of which are specific to the oblique ion bombardment: The former would lead to an increase in the number of possible nucleation sites for the CNF growth, and the C atoms arising from the latter process would migrate toward the conical tips, thus forming CNFs.

Sub-micron structuring at mesa edges

A simple process for forming sub-micron gaps between horizontal and vertical electrodes in a three-dimensional micro-electrode system without the need for high-resolution lithography is described. The process is based on the enhancement of ion milling rates in metals at oblique ion incidence, which allows the preferential erosion of metal at a mesa edge. Self-aligned electrode structures are formed on silica and oxidised silicon mesas, and electrode separations of 150–300 nm are demonstrated in geometries that may be suitable for vertical knife-edge field emission sources.

Importance of ion beam parameters on self-organized pattern formation on semiconductor surfaces by ion beam erosion

Ion beam sputtering i.e. the removal of material from a surface due to the impact of energetic ions or atoms, is an inherent part of numerous surface processing techniques. Due to self-organization caused by the process of low-energy ion beam erosion, nanostructures with different shape and high order arrangement can be evolved. In this work, results for Ar + ion beam erosion of silicon and III/V semiconductor surfaces under oblique ion incidence with simultaneous sample rotation are presented. The evolution of the surface topography and patterns are analyzed by scanning force microscopy (AFM). Especially, the influence of different settings of the used Kaufman-type broad beam ion source on nanostructures is discussed. The ion beam is extracted and formed by a multiaperture two-grid system. Beside the ion energy, the divergence of the ion beam as well as the angular distribution of the ions within the ion beam can influence the pattern formation. By a careful adjustment of the individual ion source settings regular nanopatterns on various surfaces can be achieved. Examples are given for InP, GaSb, InAs, and Si.