Low Ion Beam Research Articles

Nitrogen ion beam synthesis of InN in InP(100) at elevated temperature

The InN phase is grown in crystalline InP(100) substrates by 50keV N+ implantation at an elevated temperature of 400°C followed by annealing at 525°C in N2 ambient. Crystallographic structural and Raman scattering studies are performed for the characterization of grown phases. Temperature- and power-dependent photoluminescence studies show direct band-to-band transition peak ∼1.06eV at temperatures ⩽150K. Implantations at an elevated temperature with a low ion beam current and subsequent low temperature annealing step are found responsible for the growth of high-quality InN phase.

Exploiting the third dimension in nanofabrication technology with scanned high energy ion beams

Focussed ion beam techniques are powerful tools to fabricate and obtain images of nanostructures. Here we propose to study and create nanostructures by implantation of focussed high energy heavy ions. For this purpose we are developing and building at the new 5MV tandem accelerator of the Universidad Autónoma de Madrid, a facility capable of delivering beams focussed to a diameter below 10nm that can be scanned over the sample. This contrasts with previous methods which use keV ions. As a consequence, structures with small lateral size and a much larger perpendicular size like patterns of columns, can be created. These are expected to allow a high packing density of functional units, and other specific advantages.The nanobeam will be used mainly to create nanostructures by irradiation with heavy ions with an energy of 20–50MeV in a precise pattern (ion beam lithography), since it takes only one or few ions per spot to create structural, electronic, magnetic or chemical changes in certain materials along the ions tracks and therefore, very low ion beam intensities can be applied. Structures like ordered conducting wires in insulating media or three-dimensional magnetic column structures in a diamagnetic medium can be created. The latter will be the first application of the facility, and could be developed to provide a data storage medium with Terabits/in.2 capability, drastically increasing the present storage density.The facility will also generate nanobeams of 2–10MeV protons. They will be used to develop a scanning transmission proton microscope for research of the mentioned nanostructures and the detection of defects, voids, precipitates, etc. in other thinned samples.

Surface modification of polystyrene by low energy hydrogen ion beam

Polystyrene was modified by low energy hydrogen ions in ultrahigh vacuum. The modified surfaces were analyzed in situ by x-photoelectron spectroscopy and ex situ by atomic force microscopy. Results revealed that 10 eV H + ion bombardment on polystyrene produces a cross-linked network film, while the polymer backbone remains intact and undesirable impurity (such as nitrogen, oxygen, etc) incorporation is eliminated. The as-prepared network film is just about 5–6 nm thick, but is highly resistant to chemical solvent. However, when 100 eV H + ion bombardment is used, the aromatic rings are seriously damaged and the surface of organic film is etched. This work suggests a new route to the preparation of ultrathin polymer network films.

X-ray Emission Measurement from Organic and Insulating Materials with Low Energy Ga Ion Beams

We observed a phenomenon of X-ray emission from various types of organic and insulating materials under irradiation of a low energy (30 kV) gallium ion beam. Energy dispersive X-ray spectrometer combined with a focused ion beam instrument could detect light elements with low K-shell electron excitation energy such as carbon, oxygen, fluorine, sodium and silicon. Effect of the current intensity of gallium ion beam on the normalized X-ray yield was investigated. It was found that a strong irradiation beam current could effectively enhance the normalized X-ray yield. [DOI: 10.1380/ejssnt.2006.365]

Etching effects of low energy argon ion beam on porous anodic aluminum oxide membranes

Porous anodic aluminum oxide (AAO) membranes were sputtered by 500eV argon ion ( Ar+) beam. Scanning electron microscopy and atomic force microscopy i mages show that not only the barrier layer of AAO can be easily removed by Ar+ beam sputtering, but also several categories of surface morphologies w ere got by changing the incidence parameters. For instance, off-normal incidence bombardment results in ripple formation on the surface of AAO and off-normal in cidence during smple stage rotation leads to AAO surface smoothing. Theory of ri pple formation and evolution on amorphous substrate under ion beam irradiation d eveloped by Bradley and Harper is used to interpret the characteristics of rippl es on AAO surface.

Production of light radioactive ion beams (RIB) using inverse kinematics

At Nuclear Science Centre (NSC), New Delhi, we have implemented a facility to produce low energy light radioactive ion beams (RIBs) using (p,n) type of reactions in inverse kinematics. For this purpose primary beams from the 15-UD Pelletron accelerator impinged on a thin polypropylene foil mounted on a rotating/linearly moving target assembly. For efficiently separating the secondary beam from primary beam, the existing recoil mass spectrometer (RMS) HIRA was operated with new ion optics. Suitable hardware modifications were also made. Using this facility, we have extracted a 7Be beam of purity better than 99% and spot-size ∼4mm in diameter. This 7Be beam has been utilized in a variety of experiments in the energy range of 15–22MeV. Typical beam parameters are: intensity 104 pps, angular spread ±30mrad and energy spread ±0.5MeV. Development of appropriate detector setup/target arrangement were also made to perform these experiments. In this paper, we describe the implementation of this project.

Effect of the gas mixing technique on the plasma potential and emittance of the JYFL 14 GHz electron cyclotron resonance ion source

The effect of the gas mixing technique on the plasma potential, energy spread, and emittance of ion beams extracted from the JYFL 14 GHz electron cyclotron resonance ion source has been studied under various gas mixing conditions. The plasma potential and energy spread of the ion beams were studied with a plasma potential instrument developed at the Department of Physics, University of Jyväskylä (JYFL). With the instrument the effects of the gas mixing on different plasma parameters such as plasma potential and the energy distribution of the ions can be studied. The purpose of this work was to confirm that ion cooling can explain the beneficial effect of the gas mixing on the production of highly charged ion beams. This was done by measuring the ion-beam current as a function of a stopping voltage in conjunction with emittance measurements. It was observed that gas mixing affects the shape of the beam current decay curves measured with low charge-state ion beams indicating that the temperature and∕or the spatial distribution of these ions is affected by the mixing gas. The results obtained in the emittance measurements support the conclusion that the ion temperature changes due to the gas mixing. The effect of the energy spread on the emittance of different ion beams was also studied theoretically. It was observed that the emittance depends considerably on the dispersive matrix elements of the beam line transfer matrix. This effect is due to the fact that the dipole magnet is a dispersive ion optical component. The effect of the energy spread on the measured emittance in the bending plane of the magnet can be several tens of percent.

Ion-beam nano-patterning by using porous anodic alumina as a mask

Anodized aluminium oxide (AAO) with self-organized and ordered nano-hole arrays may bea good candidate for an irradiation mask to modify the properties of a nano-scaleregion. In order to use AAO as a mask for ion beam patterning, the ion beamtransmittance of AAO should first be tested. In an AAO with a high aspect ratio (about100), anodized from Al bulk foil, the ion beam transmittance was extremely low.However, when AAO with low aspect ratio (about 5), fabricated with thin film Al onSiO2, was irradiated with 80 keV Co ions, the Co ion transmittance was enormouslyimproved. After selective etching of the unirradiated region, ion beam patterned 80 nmSiO2 dot arrays have been fabricated. This shows a potential of AAO with a low aspect ratio foran ion beam patterning nano-mask. In order to demonstrate the ion beam nano-patterning,magnetic nano-patterning was performed. A Co/Pt multilayer film with a perpendicularmagnetic anisotropy was ion irradiated through an AAO mask with a low aspect ratio,460 nm height and 50 nm diameter, and the magnetic properties were investigatedby MOKE. The formation of a magnetic nano-pattern was confirmed by MFM.

Interactions of argon cluster ion beams with silicon surfaces

The formation of irradiation damage for Si(0 0 1) surfaces by Ar cluster ion beams at different acceleration voltages was investigated by utilizing the Rutherford backscattering spectrometry (RBS) measurement. For the peak size of 10 000 atoms per cluster, the Si surfaces had no damage by the irradiation of the cluster ions, when the acceleration voltages were less than 5 kV. Furthermore, for the acceleration voltages larger than 5 kV, the amount of displacement atoms increased with an increase of the acceleration voltage. On the other hand, when the cluster size decreased, the threshold voltage for the damage formation decreased, and it was 2 kV for the peak size of 3000 atoms per cluster. To be compared with the experimental results, molecular dynamic (MD) simulation was used, and it showed that the irradiation of Ar cluster ions with large size and low incident energy did not produce any damage on the Si surfaces. In addition, the Si surfaces, which were previously damaged at a dose of 1 × 10 15 ions/cm 2 by the irradiation of high energy cluster ion beams such as 5 keV ion beams, were re-irradiated at a dose of 1 × 10 16 ions/cm 2 by low energy cluster ion beams such as 2 keV ion beams. The RBS channeling showed that the number of displacement atoms on the damaged surface decreased. The deposited energy on the Si surface was used to improve the crystalline state of the damaged surface, which suggests that the cluster ion irradiation has the ability to anneal the solid surfaces by adjusting the acceleration voltage and the cluster size.

Fabricating Microbolometer Array on Unplanar Readout Integrated Circuit

In this paper, the integration of an experimental 32 × 32 uncooled IR microbolometer array with an unplanar CMOS Readout Integrated Circuit (ROIC) is presented. A vanadium oxide film fabricated by low temperature reactive ion beam sputtering is utilized as thermal-sensitive material in the bolometric detectors Before the integration, the unplanar ROIC for commercial use is first planarized by bisbenzocyclobutene film, then a electroless nickel-plating on ohmic contact areas is accomplished. Finally the bolometer array is fabricated using a micromachining process, which is completely compatible with CMOS technology. Measurements and calculations for the as-fabricated samples show that the responsivity of 1.4 × 104 V/W and the detectivity of 2.1 × 108cmHz1/2W−1 and a thermal response time of 10ms are obtained at a pulse bias of IV.

Reactive Ion Beams Sputtering of Vanadium Oxides Films for Uncooled Microbolometer

Vanadium oxides thin films for uncooled bolometric detectors have been fabricated on Si3N4-film-coated Si substrates by low temperature reactive ion beam sputtering in a controlled oxygen atmosphere. The typical growth temperature is kept at 200°C during sputtering, which is compatible with the post-CMOS technology. The as-deposited film exhibits sheet resistance and temperature coefficient resistant of 32 kΩ and −0.025 K−1 at room temperature, respectively.

Second order nonlinear optical properties of zinc oxide films deposited by low temperature dual ion beam sputtering

We investigated second order optical nonlinearity of zinc oxide thin films, grown on glass substrates by the dual ion beam sputtering technique under different deposition conditions. Linear optical characterization of the films was carried out by spectrophotometric optical transmittance and reflectance measurements, giving the complex refractive index dispersion. Resistivity of the films was determined using the four-point probe sheet resistance method. Second harmonic generation measurements were performed by means of the Maker fringes technique where the fundamental beam was originated by nanosecond laser at λ=1064nm. We found a relatively high nonlinear optical response, and evidence of a dependence of the nonlinear coefficient on the deposition parameters for each sample. Moreover, the crystalline properties of the films were investigated by x-ray diffraction measurements and correlation with second order nonlinearity were analyzed. Finally, we investigated the influence of the oxygen flow rate during the deposition process on both the second order nonlinearity and the structural properties of the samples.

The fabrication and high temperature stability of biaxially textured Ni tape by ion beam structure modification method

For the conventional rolling assisted biaxially textured metallic substrate (RABiTS) process, a large degree of cold rolling deformation and a subsequent high temperature annealing procedure are required to obtain adequately biaxially textured Ni tape. Recently, we have reported a newly developed process, named as ion beam structure modification (ISM), for fabricating biaxially textured Ni tape by use of low energy argon ion beam bombardment. In this paper, the biaxial texture of ISM processed Ni tape and its thermal stability at high temperatures are investigated. Results show that Ni tape processed under optimum ISM conditions, the (2 0 0) rocking curve FWHM is less than 5.7°, and the (1 1 1) φ-scan FWHM is less than 7.5°. High temperature annealing does not impair the biaxial-texture already developed in ISM processed Ni foils, although ISMs should not be regarded as a complete equilibrium process.

Generation and transport of a low energy intense ion beam

The paper describes experiments on the generation and transport of a low energy (70–120 keV), high intensity (10–30 A/cm2) microsecond duration H+ ion beam (IB) in vacuum and plasma. The IB was generated in a magnetically insulated diode (MID) with an applied radial B field and an active hydrogen-puff ion source. The annular IB, with an initial density of ji∼10–20 A/cm2 at the anode surface, was ballistically focused to a current density in the focal plane of 50–80 A/cm2. The postcathode collimation and transport of the converging IB were provided by the combination of a “concave” toroidal magnetic lens followed by a straight transport solenoid section. With optimized MID parameters and magnetic fields in the lens/solenoid system, the overall efficiency of IB transport at the exit of the solenoid 1 m from the anode was ∼ 50% with an IB current density of 20 A/cm2. Two-dimensional computer simulations of post-MID IB transport supported the optimization of system parameters.

TiN thin films deposited by ion beam sputtering: effects of energetic particles bombardment

The low energy broad argon ion beam (1.35–2.0) keV was used for sputtering of a Ti target in an atmosphere of nitrogen gas to form TiN films. During deposition the growing thin film was under argon ion irradiation from the beam periphery. The influence of the ion beam energy ( E b) and average energy delivered by assisting ions to condensing film atoms ( E n) on TiN film properties was investigated. The titanium nitride thin films were deposited at a low working pressure of 1×10 −4 mbar and at ambient substrate temperature. XRD analysis revealed the formation of a δ-TiN phase with preferred (220) orientation for the stoichiometric composition of TiN films (RBS). The increase of both the intensity of the (220) peak and TiN film crystallite dimension with increasing the energy of Ti target bombarding Ar + ions ( E b) was observed. By increasing the average ion energy per deposited metal atom ( E n) the (220) peak intensity and crystallite dimension decrease and a complete loss of (220) orientation at E n close to 162 eV/at was found. In the range of E n considered, the TiN films grain size decreases leading to the nano-structured surface as revealed by the STM analysis. The incident angle and energy of the assisted bombarding strongly influence the film-preferred orientation and sub-microstructure.

ECRIS charge breeding: High resolution spectra and emittance

The charge breeding process, consisting of a low charge state ion beam (1+) plasma capture followed by a multi-ionization process, has been developed for more than ten years in LPSC Grenoble (previously ISN) using ECRIS. The challenge has been to optimize the 1+ capture and then the reextraction of the multicharged ions produced, keeping a “reasonable ECRIS working.” There are now three ECRIS PHOENIX Booster in the world (LPSC-Grenoble, CLRC-Daresbury, and TRIUMF-Vancouver). The LPSC-ECRIS has recently been set up in a completely renewed test bench equipped with a high resolution n+ mass spectrometer and a high resolution emittance meter. The CLRC-ECRIS is dedicated to online experiments with radioactive ions at REX-ISOLDE and the TRIUMF-ECRIS will soon be ready to undergo a validation process. We will present the preliminary results obtained with the new setup of the LPSC PHOENIX Booster with a special attention to the 1+ emittance and the characterization of the unwanted beams (usually called “impurities” by the RIB production specialists) present in a spectrum of a non-UHV ECRIS.

A radioactive target/ion source for material research

A radioactive target/ion source for material research has been developed at China Institute of Atomic Energy, China. With a proton ion beam from the HI-13 tandem as the primary beam, the low intensity radioactive ion beam is generated on line. The first aim of the source is to produce a radioactive ion beam of Zn+62 which will serve as nuclear probe in material research. The main features and current status of the source are presented in this article.

Structural and optical study of GaMnAs/GaAs

GaMnAs/GaAs was obtained with mass-analyzed low energy dual ion beam depostion technique with Mn ion energy of 1000 eV and a dose of 1.5 × 1018 Mn+/cm2 at the substrate temperature of 400°C and was annealed at 840°C. X-ray diffraction spectra showed that Ga5.2Mn, Ga5Mn8, α-Mn and Mn3Ga were obtained in the as-grown sample. After annealing Mn3Ga and α-Mn disappeared, Ga5Mn8 tended to disappear, Ga5.2Mn crystallized better and new phase of Mn2As was generated. The photoluminescence spectra of the as-grown sample showed that the 1.5042 eV GaAs exciton peak, 1.4875 eV peak involving a carbon acceptor and a broad band near 1.35 eV. After annealing at 840°C, the 1.5042 eV peak and 1.4875 eV shifted to 1.5065 and 1.4894 eV, respectively, and the photoluminescence intensity of the 1.35 eV band increased greatly.

P‐105: Out‐of‐Plane Alignment Properties of Nematic Liquid Crystals on Polyimide Surface Bombarded by Ar Ion Beam

AbstractPolyimide surfaces bombarded by a low energy argon ion beam align liquid crystals parallel to ion beam exposure direction. By ion beam conditions, such as the energy of the incident ions, the angle of incidence and exposure time, the unidirectional out‐of‐plane liquid crystal (LC) tilt angle is changed. These are related with the remaining π‐bond of polyimide which is not destroyed by ion beam bombardment. For application in LCDs, unit cells fabricated by ion beam alignment method are compared with one which manufactured by the rubbing method. And The TN cell fabricated by ion beam alignment method has enough retention time to apply to TFT(Thin Film Transitor) LCDs

(Ga,Mn,N) compounds growth with mass-analyzed low energy dual ion beam deposition

The (Ga,Mn,N) samples were grown by the implantation of low-energy Mn ions into GaN/Al 2O 3 substrate at different elevated substrate temperatures with mass-analyzed low-energy dual ion beam deposition system. Auger electron spectroscopy depth profile of samples grown at different substrate temperatures indicates that the Mn ions reach deeper in samples with higher substrate temperatures. Clear X-ray diffraction peak from (Ga,Mn)N is observed in samples grown at the higher substrate temperature. It indicates that under optimized substrate temperature and annealing conditions the solid solution (Ga,Mn)N phase in samples was formed with the same lattice structure as GaN and different lattice constant.