Ar Ion Beam Research Articles

Magnesium diboride nanobridges fabricated by electron-beam lithography

MgB 2 nanobridges were fabricated by e-beam lithography and Ar-ion beam milling. Nanobridges of widths ranging from 60 nm to 1μm and 3μm in length were realized by Ar-ion beam milling using amorphous carbon as etching mask. The processing did not harm the superconducting properties appreciably. High values of the critical current density, more than 10MA∕cm2, were measured for bridges with widths down to 60 nm. Current-voltage (I-V) characteristics showed a behavior typical of a bridge going normal, after the critical current is exceeded, and remaining normal as the current is decreased to a lower switch back value due to Joule heating. We could also observe switching behavior in some bridges indicating formation of normal hotspots in the bridges before they returned to their superconducting state. Alternative explanations may include natural grain boundaries in the film or the movement of Abrikosov vortices. The current-voltage (I-V) characteristics showing critical current densities up to 5×107⁢A∕cm2 indicates excellent film properties in the nanobridges.

Interactions of ethanol cluster ion beams with silicon surfaces

The liquid cluster ion beam system was developed, in which cluster ions of organic molecules such as ethanol could be produced. In order to investigate the interactions of ethanol cluster ion beams with solid surfaces, SiO2 substrates and SiO2 films were irradiated at different acceleration voltages. The sputtered depth increased exponentially with the acceleration voltage. When the acceleration voltage was 9kV, the sputtered depths of Si and SiO2 at a dose of 1×1016ions/cm2 were 344.6nm and 47.2nm, respectively. The sputtering yield for the Si surface was approximately 100 times larger than that by Ar ion beams. With regards to the sputtering ratio of Si to SiO2, the ratio increased with decreasing acceleration voltage. This suggests that chemical reactions between Si and ethanol produced silicon hydride which was the dominant etching material for the Si surfaces.In addition, the AFM observation showed that the sputtered surface had an average roughness of less than 1nm. With regards to the crystalline state of the sputtered surface, the RBS and ellipsometry measurements were performed, and they showed that the Si surface damage induced by ethanol cluster ion irradiation was less than that by Ar monomer ion irradiation. Thus, Si surfaces etched at high sputtering speed by ethanol cluster ion beams had a lower damage and an atomically flat surface.

Nanostructuring polymers by soft lithography templates realized via ion sputtering

We demonstrate that a combination of ion sputtering and soft lithography is an alternativeand effective way of nanostructuring soft matter. We create self-organized nanoscalestructures on a glass template by irradiating the surface with a defocused, low energy Arion beam. Capillary force lithography is then used to transfer the pattern, exploiting theglass transition of polymeric layers. In particular, we demonstrate the pattern transfer of aperiodic 150 nm ripple structure onto an organic compound. This new, unconventionalcombination is then a low-cost strategy that opens the way to a variety of applications inthe field of organic-based devices.

Band Alignment at CdS/wide-band-gap Cu(In,Ga)Se2Hetero-junction by using PES/IPES

Direct characterization of band alignment at chemical bath deposition <TEX>$(CBD)-CdS/Cu_{0.93}(In_{1-x}Ga_x)Se_2$</TEX> has been carried out by photoemission spectroscopy (PES) and inverse photoemission spectroscopy (IPES). Ar ion beam etching at the condition of the low ion kinetic energy of 400 eV yields a removal of surface contamination as well as successful development of intrinsic feature of each layer and the interfaces. Especially interior regions of the wide gap CIGS layers with a band gap of <TEX>$1.4\~1.6\;eV$</TEX> were successfully exposed. IPES spectra revealed that conduction band offset (CBO) at the interface region over the wide gap CIGS of x = 0.60 and 0.75 was negative, where the conduction band minimum of CdS was lower than that of CIGS. It was also observed that an energy spacing between conduction band minimum (CBM) of CdS layer and valance band maximum (VBM) of <TEX>$Cu_{0.93}(In_{0.25}Ga_{0.75})Se_2$</TEX> layer at interface region was no wider than that of the interface over the <TEX>$Cu_{0.93}(In_{0.60}Ga_{0.40})Se_2$</TEX> layer.

Formation of biaxial texture in metal films by selective ion beam etching

The formation of in-plane texture via ion bombardment of uniaxially textured metal films was investigated. In particular, selective grain Ar ion beam etching of uniaxially textured (0 0 1) Ni was used to achieve in-plane aligned Ni grains. Unlike conventional ion beam assisted deposition, the ion beam irradiates the uniaxially textured film surface with no impinging deposition flux. The initial uniaxial texture is established via surface energy minimization with no ion irradiation. Within this sequential texturing method, in-plane grain alignment is driven by selective etching and grain overgrowth. Biaxial texture was achieved for ion beam irradiation at elevated temperature.

Formation of silver incorporated calcium phosphate film for medical applications

Calcium phosphate coating layers were formed by electron beam evaporation of hydroxyapatite as an evaporant with and without simultaneous Ar ion bombardments. The Ca/P ratio of film, which determined the biological properties, was controlled by ion beam current. Without ion beam bombardments, the film had the low Ca/P ratio of 1.30, however, the ratio increased to 2.02 by bombarding of Ar ion beam extracted from the end-hall type ion gun set to 0.6A. Silver incorporated calcium phosphate films were formed by immersing calcium phosphate coated samples in 0.4M AgNO3 for 30min, and the Ag doped surface was almost 100% effective in reducing bacteria on contact with respect to controls.

Application of highly charged Ar ion beams to ion beam lithography

Ion beam lithography (IBL) is a very useful tool for the fabrication of nano-structures. In order to expand the applicability of IBL by using highly charged ions (HCI), Ar1+ and Ar9+ ions were irradiated onto spin-on-glass (SOG) through a stencil mask. The step structure was successfully fabricated on SOG by the chemical etching after the irradiation. The depth of etching of the SOG using the Ar9+ ions increases linearly with dose and was greater than the etching depth obtained using Ar1+ ions. The maximum etching depth of the SOG using Ar9+ ions was larger than the range calculated by the SRIM code. The results show the effectiveness of HCI for IBL and indicate the contribution of the damage created by indirect irradiation processes.

Progress in the production of CsI and diamond thin film photocathodes

The comparison between the quantum efficiency of photocathodes coated with thin CsI films obtained by thermal evaporation and, for the first time, by Ar ion-beam sputtering is reported. The sensitivity of photocathodes has been found to be strongly dependent on the morphology and roughness of the evaporated and sputtered CsI films. The effect of surface roughness on four different substrates has been investigated and is discussed. Preliminary measurement results on the photoemissivity of diamond films are also given.

Fullerenelike arrangements in carbon nitride thin films grown by direct ion beam sputtering

Carbon nitride (CNx) thin films were grown by direct N2∕Ar ion beam sputtering of a graphite target at moderate substrate temperatures (300–750K). The resulting microstructure of the films was studied by high-resolution transmission electron microscopy. The images showed the presence of curved basal planes in fullerenelike arrangements. The achievement and evolution of these microstructural features are discussed in terms of nitrogen incorporation, film-forming flux, and ion bombardment effects, thus adding to the understanding of the formation mechanisms of curved graphitic structures in CNx materials.

Free-standing epitaxial La1−x(Sr,Ca)xMnO3 membrane on Si for uncooled infrared microbolometer

Ar ion beam etching and inductively coupled SF6 and C4F8 plasma-etching processes have been employed to fabricate free standing membrane from the heteroepitaxial La1−x(Sr,Ca)xMnO3(50nm)∕Bi4Ti3O12(100nm)∕CeO2(40nm)∕YSZ(30nm) film structure pulsed laser deposited on Si(001) wafer. We demonstrate feasibility to use epitaxial colossal magnetoresistive manganite film as thermally isolated self-supporting membrane for uncooled infrared microbolometer applications.

Ion bombardment-induced high orientation of Al/Ti films for surface acoustic wave device applications

Al/Ti films were deposited on 128° Y-X LiNbO3 substrates by electron-beam (e-beam) deposition. Low-energy Ar ion beam bombardment was employed during the Ti underlayer deposition. Influence of low-energy beam bombardment on the texture of Al/Ti films was investigated by x-ray diffraction (XRD) analysis. It was found that Al films deposited on Ar-ion bombarded Ti underlayers possessed excellent (111) texture. With the textured Al/Ti films, a 2.3-GHz range image-impedance connection surface acoustic wave (SAW) filter was successfully fabricated.

Flux effect on the ion-beam nitriding of austenitic stainless-steel AISI 304L

The effect of flux and Ar pretreatment during ion-beam nitriding of austenitic stainless steel is investigated. The ion energy and temperature were 1.2keV and 400°C, respectively, the ion current densities were 0.5, 0.67, and 0.83mAcm−2. The nitrogen distribution profiles were measured using nuclear reaction analysis. The obtained nitrogen distribution profiles were analyzed by the means of the nitrided layer thickness evolution due to sputtering and diffusion and the model of trapping–detrapping. Both approaches could fit well the experimental results, however, different diffusion coefficients have to be assumed for each current density. In addition, the diffusion coefficients are higher for higher current densities. On the other hand, it is shown that the pretreatment with Ar-ion beam at nitriding temperatures produces only a thermal effect without any other influence on the following nitrogen diffusion. The results are discussed in relation with surface and temperature effects and atomic transport mechanisms.

Ion-Beam Induced Liquid Crystal Alignment on Diamond-like Carbon and Fluorinated Diamond-like Carbon Thin Films

Homogeneous and homeotropic orientations of nematic liquid crystal (NLC) are investigated on various inorganic thin films which are exposed to Ar ion-beam. It is the novel investigations which results in a completely dry processing technique for both the thin film deposition and alignment steps. In the case of homogenous alignment on diamond-like carbon (DLC) layer, optical band gap and the polar surface energy are investigated in order to elucidate the alignment mechanism by ion beam (IB) irradiation. We elucidate the role of surface polarity in DLC films with respect to the LC orientation. On the other hand, FDLC thin films are selected by homeotropic alignment layer with regard to the relationship between surface tension and LC orientation. Selected pretilt angles in the range of 71.1–89.8° can be easily obtained with ion beam irradiation. It is sensitively changed by thin films composition and the angle of ion beam irradiation.

Carbon nanotube growth for field-emission cathodes from graphite paste using Ar-ion bombardment

Multiwall carbon nanotubes (MW-CNT) have been synthesized from solid-phase graphite. The graphite is deposited as a thick-film paste and irradiated with a 1.2keV flood Ar-ion beam, transforming the graphite surface to a composite of MW-CNT embedded in the graphite matrix. Micro-Raman measurements have verified that the nanotubes are metallic in nature. The technique was used to make printed field-emission cathodes. Emission from these cathodes demonstrates Fowler–Nordheim tunneling characteristics. The irradiated film emits at an extraction field of 5.0V∕μm, which is less than one-sixth of the minimum extraction field of the nonirradiated graphite film, and exhibit lower noise and greater emission uniformity.

Ion beam erosion of amorphous materials: evolution of surface morphology

In this work we present our results concerning the formation of self-organized nanoscale structures during the bombardment with a low-energy defocused Ar ion beam. We studied glass surfaces because of their physical properties, technological interest and cheapness. The evolution of sample surface was studied ex situ by atomic force microscopy. We found, in agreement with Bradley and Harper, a morphology characterized by a regular ripple structure with the wave vector perpendicular or parallel to the ion beam direction. This structure periodicity was found to vary in the range 90–350nm with a linear time evolution. In order to gain further information about the sputtering process and for comparison with the existing continuum theories of surface erosion, we studied the scaling behaviour of surface roughness.

태양전지용CuInSe2와 CuGaSe2흡수층의 전자구조해석을 위한 표면 청정기술 개발

Two kinds of physical treatments were examined for the analysis both of intrinsic surface and interior nature of CuInS <TEX>$e_2$</TEX>[CIS] and CuGaS <TEX>$e_2$</TEX>[CGS] films grown in separated systems. For the first method, a selenium protection layer which was immediately deposited after the growth of the CIS was investigated. The Se cap layer protects CISe surface from oxidation and contamination during the transport under ambient atmosphere. The Se cap was removed by thermal annealing at temperature above 15<TEX>$0^{\circ}C$</TEX>. After the decapping treatment at 2<TEX>$25^{\circ}C$</TEX> for 60 min, ultraviolet photoemission and inverse photoemission measurements of the CIS film showed that its valence band maximum(VBM) and conduction band minimum (CBM) are located at 0.58 eV below and 0.52 eV above the Fermi level <TEX>$E_{F}$</TEX>, respectively. For the second treatment, an Ar ion beam etching was exploited. The etching with ion kinetic energy <TEX>$E_{k}$</TEX> above 500 eV resulted in broadening of photoemission spectra of core signals and occasional development of metallic feature around <TEX>$E_{F}$</TEX>. These degradations were successfully suppressed by decreasing <TEX>$E_{k}$</TEX> below 400 eV. CGS films etched with the beam of <TEX>$E_{k}$</TEX> = 400 eV showed a band gap of 1.7 eV where <TEX>$E_{F}$</TEX> was almost centered.st centered.

Band alignment at CdS/wide-band-gap Cu(In,Ga)Se2 hetero-junction by using PES/IPES

AbstractDirect characterization of band alignment at chemical bath deposition (CBD)-CdS/Cu0.93 (In1-xGax)Se2 has been carried out by photoemission spectroscopy (PES) and inverse photoemission spectroscopy (IPES). Ar ion beam etching at the condition of the low ion kinetic energy of 350 eV yields a removal of surface contamination as well as successful measurement of the intrinsic properties of each layer and the interfaces. Especially interior regions of the wide gap CIGS layers with a band gap of 1.4 ∼ 1.6 eV were successfully exposed. IPES spectra revealed that the conduction band offset (CBO) at the interface region of the wide gap CIGS with x = 0.60 and 0.75 was negative, where the conduction band minimum of CdS was lower than that of CIGS. It was also observed that the energy spacing between conduction band minimum (CBM) of CdS layer and valence band maximum (VBM) of Cu0.93(In0.25Ga0.75)Se2 layer at interface region was no wider than that of the interface over the Cu0.93(In0.60Ga0.40)Se2 layer.

MFM Images and Micromagnetic Simulation of Submicron-Sized Single-Crystal Co particles

Submicron-sized Co particles were fabricated by patterning single-crystal Co thin films, and their magnetic domain structures were observed by magnetic force microscopy (MFM). The Co films (250 nm in thickness) were epitaxially deposited onto Al2O3 (001) single-crystal substrates by electron beam evaporation, and from thesefilms (with their c-axis parallel to the surface normal) circular dots with diameters of 0.5, 1, and 2.5 1μm were patterned by electron beam lithography and Ar ion beam etching. All the dots fabricated proved to suffer from side wall etching, resulting in cone shapes in the case of 0.5μ and 1μm diameters. In dots with diameters of 1 and 2.5μm, maze patterns in domain structure were clearlμEobserved, whereas concentric contrast became dominant in 0.5μm dots. Numerical simulation based on the Landau-Lifshitz-Gilbert equation revealed that these dotspossess components of both perpendicular and vortexmagnetization simultaneously.

Ion-beam sputtering deposition of CsI thin films

Stoichiometric CsI thin films were deposited by Ar ion-beam sputtering of a CsI target at room temperature. The sputtered 100-nm thick CsI films obtained were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM) and quantum efficiency (QE) measurements. As it was expected, the chemical, morphological, crystalline and photo-emissive properties of CsI films obtained depended on the deposition parameters. Comparison with results obtained for evaporated CsI films indicated that surface morphology, i.e., the effective photo-emissive surface area, is one of the important parameters in influencing the QE .

High Temperature Superconducting Thin Film Josephson Junctions

High-temperature superconducting YBa2Cu3Ox (YBCO) thin films (120 nm thick) were used to prepare YBCO/B/YBCO Josephson ramp-type junctions with tunneling barrier (B) performed by Ar ion beam modification of the ramp area surface. After the sample transportation into a high vacuum deposition chamber the amorphised ramp surface was annealed and then the YBCO counter electrode was sputtered. The area of the ramp-type YBCO junction was determined by a photoresist mask and Ar ion beam etching. Current voltage characteristics and current steps during irradiation of the samples by microwaves confirmed the presence of Josephson effect in the made structures.