Development of procedures for programmable proximity aperture lithography

Abstract Programmable proximity aperture lithography (PPAL) with MeV ions has been used in Jyvaskyla and Chiang Mai universities for a number of years. Here we describe a number of innovations and procedures that have been incorporated into the LabView-based software. The basic operation involves the coordination of the beam blanker and five motor-actuated translators with high accuracy, close to the minimum step size with proper anti-collision algorithms. By using special approaches, such writing calibration patterns, linearisation of position and careful backlash correction the absolute accuracy of the aperture size and position, can be improved beyond the standard afforded by the repeata…

Fast and blister-free irradiation conditions for cross-linking of PMMA induced by 2MeV protons

For soft lithography, the conventional negative tone resists, such as SU-8, that are used to create the mold have a number of drawbacks. PMMA, which is normally used as a positive tone resist, can be used as a negative resist by using high-fluence irradiation conditions. In this report, we outline optimization of the irradiation conditions for PMMA thin films using 2MeV H^+ ions to exploit their ability to work as a negative tone resist at ion fluences above 1.0x10^1^5ionscm^-^2. The main aim was to induce cross-linking while maintaining the exposed regions free of blisters and maintaining short irradiation times. We found that by using a two-step process with a low-flux irradiation, follow…

Influence of titanium-substrate roughness on Ca–P–O thin films grown by atomic layer deposition

Abstract Amorphous Ca–P–O films were deposited on titanium substrates using atomic layer deposition, while maintaining a uniform Ca/P pulsing ratio of 6/1 with varying number of atomic layer deposition cycles starting from 10 up to 208. Prior to film deposition the titanium substrates were mechanically abraded using SiC abrasive paper of 600, 1200, 2000 grit size and polished with 3 μm diamond paste to obtain surface roughness R rms values of 0.31 μm, 0.26 μm, 0.16 μm, and 0.10 μm, respectively. The composition and film thickness of as-deposited amorphous films were studied using Time-Of-Flight Elastic Recoil Detection Analysis. The results showed that uniform films could be deposited on ro…

Advanced time-stamped total data acquisition control front-end for MeV ion beam microscopy and proton beam writing

Many ion-matter interactions exhibit [email protected] time dependences such as, fluorophore emission quenching and ion beam induced charge (IBIC). Conventional event-mode MeV ion microbeam data acquisition systems discard the time information. Here we describe a fast time-stamping data acquisition front-end based on the concurrent processing capabilities of a Field Programmable Gate Array (FPGA). The system is intended for MeV ion microscopy and MeV ion beam lithography. The speed of the system (>240,000 events s^-^1 for four analogue to digital converters (ADC)) is limited by the ADC throughput and data handling speed of the host computer.

A gas ionisation Direct-STIM detector for MeV ion microscopy

Abstract Direct-Scanning Transmission Ion Microscopy (Direct-STIM) is a powerful technique that yields structural information in sub-cellular whole cell imaging. Usually, a Si p-i-n diode is used in Direct-STIM measurements as a detector. In order to overcome the detrimental effects of radiation damage which appears as a broadening in the energy resolution, we have developed a gas ionisation detector for use with a focused ion beam. The design is based on the ETH Frisch grid-less off-axis Geiger–Muller geometry. It is developed for use in a MeV ion microscope with a standard Oxford Microbeams triplet lens and scanning system. The design has a large available solid angle for other detectors …

Nanoscale Engineering in the Biosciences

Biological matter is one of the most diverse and important classes of materials. Products of living organisms (wood, bone, cotton, wool, leather, coal, oil, drugs, etc.) are vital to humanity as foodstuffs, energy sources, engineering and construction materials, and chemicals; and by the way, they shape the environment of the biosphere.

Ion-sputtering deposition of Ca–P–O films for microscopic imaging of osteoblast cells

Abstract An ion-beam sputtering technique was used to produce Ca–P–O films on borosilicate glass at room temperature from hydroxyapatite targets using nitrogen, argon and krypton beams at different acceleration voltages. The sputtering target was pressed from high purity hydroxyapatite powder or mixture of high purity hydroxyapatite powder and red phosphorus in order to optimise the film composition. The film composition, determined using time-of-flight elastic recoil detection analysis (TOF–ERDA), was found to be strongly dependent on the ion energy used for deposition. By extra doping of the target with P the correct Ca/P atomic ratio in the deposited films was reached. The films deposite…

Synthesis and characterization of cobalt silicide films on silicon

Cobalt silicide has emerged as a leading contact material in silicon technology due to its low resistivity, high stability and small lattice mismatch. In this study, 0.2-0.4 mu m thick Co films were deposited on Si(100) wafers by RF magnetron sputtering at room temperature, and annealed at temperatures from 600 to 900 degrees C in vacuum. As-deposited and annealed samples were characterized by Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Although the Si substrates were sputter cleaned before the deposition, all the samples showed a thin oxide layer at the Si/Co interfaces. Annealing up to 700 d…

Box 5: Surface Crystallography Terminology

The crystalline nature of the surface differs from the bulk because atoms on the surface experience a different force field due to unterminated bonds, oxidation by adatoms etc. [1]. Free energy minimisation leads to reconstruction of the surface layer from the bulk by formation of dimers and displacement of atoms from their normal sites.

Wettability and compositional analysis of hydroxyapatite films modified by low and high energy ion irradiation

Abstract Hydroxyapatite-like thin films on silicon substrate were deposited using atomic layer deposition and were subjected to irradiation with Ar ions accelerated through 0.6–1.2 kV as well as 2 MeV 16 O + ions. After low energy Ar irradiation a significant reduction in contact angle was observed. However, the Ca/P atomic ratio remained unchanged. No reduction in contact angle was seen for high energy 16 O + irradiation. Atomic force microscopy showed the enhancement of floral-like pattern after low energy Ar bombardment while high energy oxygen irradiation lead to raised islands on as-deposited films.

Objective improvement of the visual quality of ion microscope images

The need to operate with low ion beam fluences implies the images obtained using ion microscope (IM) are often grainy and have poor visual quality compared to what can be obtained using e.g. confocal microscopy. This results from the Poissonian distribution of counts in pixels. Here we report work on some different approaches for objectively improving the visual quality of IM images. In this work we present (i) dramatic improvement in the visual image quality of off-axis and direct-scanning transmission ion microscopy (STIM) images by suppression of zero-pixels; (ii) denoising of PIXE images using wavelet filtering and (iii) use of the feature preserving characteristics of wavelet filtering…

Adhesion of proton beam written high aspect ratio hydrogen silsesquioxane (HSQ) nanostructures on different metallic substrates

Abstract Hydrogen silsesquioxane (HSQ) behaves as a negative resist under MeV proton beam exposure. HSQ is a high-resolution resist suitable for production of tall (

Electronics for Application of Ion Beams in Nanoscience

The breadth of ion-beam nanoscience methods discussed in the proceeding chapters implies that the control and readout systems also span a wide range of techniques. For many nanoscience and technology applications the need to process or characterise a batches of samples has lead to a convergence of data acquisition systems and control systems. This coupled with the development of high-performance lowcost computing over the past decades has lead to a progressive evolution in data acquisition technology. Historically, much of the electronics used in nanoscience and technology using ion beams is based on nuclear analogue pulse counting and spectrometry where NIM (Nuclear Instrumentation Modules…

Formation of cobalt silicide from filter metal vacuum arc deposited films

The thermal reaction of Co film deposited on Si(111) surfaces by a high current filter metal vacuum arc (FMEVAD) system has been studied. After deposition the films were annealed over the 400-900 degrees C temperature range for 30 min. Rutherford backscattering spectrometry (RBS) was used to characterize the elemental depth distributions in the films subjected to different annealing temperatures. Ordered chemical phases were determined by glancing-incidence X-ray diffraction (GIXRD) and the morphology was determined by cross section transmission electron microscopy (TEM). The results show that the phases formed are Co2Si at 400 degrees C, CoSi + Coo at 500 degrees C, CoSi + CoSi2 at 600 deg…

A predictive model for the electronic stopping force for molecular dynamic simulation (I)

Abstract We have examined a predictive model for the electronic stopping force (dE/dx)e to be used in the classical molecular dynamic (MD) simulation. The essential term (dE/dx)proton of (dE/dx)e is based on the Lindhard–Winther theory, while the effective charge follows the Brandt–Kitagawa model. The (dE/dx)proton term is expressed by the electron local density ρ(r) defined by the Muffin-tin model and the Hartree–Fock–Slater approximation. This model had been proposed to explain the impact-parameter dependence of (dE/dx)e for channeling ions passing through a semiconductor. Here the energy dependence of the averaged 〈dE/dx〉e after thin-film transmission was examined, where the electron–pho…

Lithographic fabrication of soda-lime glass based microfluidics

Abstract Glass is an important material for chemical processing and analysis because of its relatively low cost, mechanical strength, chemical inertness, optical transparency, and electrical insulation and temperature resistance far beyond that of most polymeric materials. We have investigated techniques for direct writing with MeV ions on soda-lime glass as well as capping procedures to form closed buried channels suitable for high-pressure driven flow. Exposure and development of open-channel structures was studied using a combination of programmable proximity aperture lithography and different developers. Unlike our previous work on MeV ion beam lithography of natural silica where an 8% …

Retention of Pb isotopes in glass surfaces for retrospective assessment of radon exposure

Abstract In recent years there has been increasing interest in radio-epidemiological techniques to retrospectively measure the radon dose exposure by determining the activity of 210Pb, the longest-lived 222Rn progeny, in glass surface layers. In this study the diffusion of 39 keV 209Pb+ ions implanted into glass using the IGISOL facility has been studied under conditions that mimic the recoil implantation of 210Pb from 222Rn. The resulting depth distributions of 209Pb were then measured after heat treatment in vacuum at different temperatures by a sputter erosion technique. The diffusion coefficient could be described by an Arrhenius equation D = D0exp(−H/kT) where D 0 = 0.30 - 0.24 + 1.14 …

WITHDRAWN: Measurement of beam focus quality in biomedical nuclear microscopy.

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Why are hydrogen ions best for MeV ion beam lithography?

The exposure characteristics of poly-(methyl methacrylate) (PMMA) for 2MeV ^1H^+, 3MeV ^4He^2^+ and 6MeV ^1^2C^3^+ have been investigated. The samples were characterised using Atomic Force Microscopy (AFM), optical microscopy and Raman spectroscopy. Development was carried out using a 7:3 propan-2-ol:H"2O mixture to determine clearing and cross-linking fluences. It was found that protons had a considerably wider tolerance to exposure variations and a smaller span of doses within the ion track. Furthermore, the void formation and consequent stress-induced surface roughening were smaller for protons. For all ions, the C?C bond Raman signal increased continuously with dose and fluence, even we…

Experimental Linear Energy Transfer of Heavy Ions in Silicon for RADEF Cocktail Species

Experimental linear energy transfer values of heavy ions in silicon are presented with comparison to estimations from different semi empirical codes widely used among the community. This paper completes the experimental LET data for the RADEF cocktail ions in silicon.

Energy-loss straggling of 2-10 MeV/u Kr ions in gases

Measurements have been performed on a time-of-flight setup at the Jyväskylä K130 cyclotron, aiming at energy-loss straggling of heavy ions in gases. Theoretical predictions based on recently developed theory as well as an empirical interpolation formula predict that straggling can be more than ten times higher than Bohr straggling in the MeV/u regime. Our measurements with up to 9.3 MeV/u Kr ions on He, N2, Ne and Kr targets confirm this feature. Our calculations show the relative contributions of linear straggling, bunching including packing, and charge exchange. Our results for stopping cross sections are compatible with values from the literature. Funding Agencies|EU||Academy of Finland …

Ordering effects in extreme high-resolution depth profiling with MeV ion beams

Abstract The continuing development of depth profiling with MeV ion beam methods with depth resolutions in the nanometre, and even sub-nanometre, regime implies the resolved depth become comparable with the interatomic spacing. To investigate how short-range ordering influences depth profiles at these resolutions, we have employed a mathematical modelling approach. The radial, g ( r ) and depth distribution, g ( z ) functions were calculated for (1 0 0) surface, random and amorphous Si structures at 300 K produced using molecular dynamics simulations with the EDIP quasi-empirical potential. The results showed that short-range ordering lead to reduction of the scattering yield below the deep…

High speed microfluidic prototyping by programmable proximity aperture MeV ion beam lithography

Abstract Microfluidics refers to the science and technology for controlling and manipulating fluids that flow along microchannels. For the development of complex prototypes, many microfluidic test structures are required first. Normally, these devices are fabricated via photolithography. This technique requires a photomask for transferring a pattern to photoresists by exposing with UV light. However, this method can be slow when a new structure is required to change. This is because a series of photomasks are needed, which is time consuming and costly. Here, we present a programmable proximity aperture lithography (PPAL) technique for the development of microfluidic prototype in poly(methyl…

Exploratory nuclear microprobe data visualisation using 3- and 4-dimensional biological volume rendering tools

Abstract The emergence of Confocal Microscopy (CM) and Atomic Force Microscopy (AFM) as everyday tools in cellular level biology has stimulated development of 3D data visualisation software. Conventional 2-dimensional images of cell (optical) sections obtained in a transmission electron or optical microscopes and more sophisticated multidimensional imaging methods require processing software capable of 3D rendering and mathematically transforming data in 3-, 4-, or more dimensions. The richness of data obtained from the different nuclear microscopy imaging techniques and often parallel information channels (X-ray, secondary electron, Scanning Transmission Ion Microscopy) is often not obviou…

Energy loss and straggling of MeV Si ions in gases

We present measurements of energy loss and straggling of Si ions in gases. An energy range from 0.5 to 12 MeV/u was covered using the 6 MV EN tandem accelerator at ETH Zurich, Switzerland, and the K130 cyclotron accelerator facility at the University of Jyväskylä, Finland. Our energy-loss data compare well with calculation based on the SRIM and PASS code. The new straggling measurements support a pronounced peak in He gas at around 4 MeV/u predicted by recent theoretical calculations. The straggling curve structure in the other gases (N2, Ne, Ar, Kr) is relatively flat in the covered energy range. Although there is a general agreement between the straggling data and the theoretical calculat…

Formation of cobalt silicide films by ion beam deposition

Abstract Thin films of cobalt silicide are widely used as metallization in very large-scale integrated electronic circuits. In this study, Co ions were deposited on Si(1 1 1) wafers by a high beam current filter metal vacuum arc deposition (FMEVAD) system. Surface silicide films were formed after annealing from 500 to 700 °C for 30 min. The results show that a thin CoSi2 surface layer with both a smooth surface topography and sharp interface can be achieved by annealing at 700 °C. The CoSi phase and O contamination were observed in the samples that were annealed at lower temperatures.

Measurements of the stopping forces for heavy ions in Ge, Ag and Au using novel ‘polka-dot’ detectors

Measurements of the stopping forces for C-14, N-14 and O-16 ions in Ge and Au, for N-14 and F-19 ions in Ag, as well as for F-19 ions in Au have been made, respectively. A novel technique, reported recently, using PIN diodes coated directly with the stopping medium in a polka dot pattern was used. This provided a set of precise, self-consistent measurements on the same stopping medium. Results show small but significant deviations from SRIM stopping predictions and are also compared to a recently-developed empirical stopping force predictor.

Modification of Materials by MeV Ion Beams

Today's fast developing technological based society places ever accelerating demands for new materials and materials processing methods. Leading edge fields as diverse as biomedical tissue engineering, quantum device, optical and magnetic information storage technology as well as immobilization of actinides, all require nanoscale engineering through controlled materials modification. The evolution of these advances from the research science stage to the industrial applications is a particular challenging task. Amongst the beam processing methods for materials modification MeV ions occupy a unique place. They interact strongly with both the atomic and electronic structures of the target mate…

Mobility determination of lead isotopes in glass for retrospective radon measurements

In retrospective radon measurements, the 22-y half life of (210)Pb is used as an advantage. (210)Pb is often considered to be relatively immobile in glass after alpha recoil implanted by (222)Rn progenies. The diffusion of (210)Pb could, however, lead to uncertain wrong retrospective radon exposure estimations if (210)Pb is mobile and can escape from glass, or lost as a result of cleaning-induced surface modification. This diffusion was studied by a radiotracer technique, where (209)Pb was used as a tracer in a glass matrix for which the elemental composition is known. Using the ion guide isotope separator on-line technique, the (209)Pb atoms were implanted into the glass with an energy of …

Development of the Jyväskylä microbeam facility

Abstract A new microbeam facility is being constructed at the 1.7 MV Pelletron Accelerator in Jyvaskyla. The facility is designed for easy upgrading and incorporates a number of innovative features. Initially, it is based on a Heidelberg doublet with a design capability of a 3 × 5 μm beamspot at PIXE intensities and later upgraded to nanobeam performance. A thermal-expansion compensated rigid frame mounted on a mechanically isolated floor section is used to support the ion optical components. A compact-post focusing electrostatic deflector is used for high linearity beam scanning. This together with a novel time-stamped data collection (TDC) allows dynamic effects in IBIC, fluorescence blea…

Atomic layer deposition and characterization of biocompatible hydroxyapatite thin films

Abstract Atomic layer deposition (ALD) was used to produce hydroxyapatite from Ca(thd) 2 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionato) and (CH 3 O) 3 PO onto Si(100) and Corning (0211). Film crystallinity, stoichiometry, possible impurities and surface morphology were determined. The as-deposited films contained significant amounts of carbonate impurities however, annealing at moist N 2 flow reduced the carbonate content even at 400 °C. The as-deposited Ca–P–O films were amorphous but rapid thermal annealing promoted the formation of the hydroxyapatite phase. Mouse MC 3T3-E1 cells were used for the cell culture experiments. According to the bioactivity studies cell proliferation was enhanc…

Aperture-edge scattering in MeV ion-beam lithography. I. Scattering from a straight Ta aperture edge

Collimators are widely used to define MeV ion beams. Recent studies have shown the capability of collimators to define beams of MeV ions with sub-100nm dimensions. Such nanometer beams have potential applications in MeV ion-beam lithography, which is the only maskless technique capable of producing extremely high aspect-ratio micro- and nanostructrures, as well as in high-resolution MeV ion-beam-based tomography. The ion scattering from the collimator edges that define the beam can be a resolution-restricting factor in these applications. Scattering processes at edges are difficult to study using conventional simulation codes because of the complicated geometry. In this part of the work, th…

Direct Writing of Channels for Microfluidics in Silica by MeV Ion Beam Lithography

The lithographic exposure characteristic of amorphous silica (SiO2) was investigated for 6.8 MeV16O3+ions. A programmable proximity aperture lithography (PPAL) technique was used for the ion beam exposure. After exposure, the exposed pattern was developed by selective etching in 4% v/v HF. Here, we report on the development of SiO2in term of the etch depth dependence on the ion fluence. This showed an exponential approach towards a constant asymptotic etch depth with increasing ion fluence. An example of microfluidic channels produced by this technique is demonstrated.

Charge Exchange and Electron Stripping

Fabrication of microfluidic devices using MeV ion beam Programmable Proximity Aperture Lithography (PPAL)

Abstract MeV ion beam lithography is a direct writing technique capable of producing microfluidic patterns and lab-on-chip devices with straight walls in thick resist films. In this technique a small beam spot of MeV ions is scanned over the resist surface to generate a latent image of the pattern. The microstructures in resist polymer can be then revealed using a chemical developer that removes exposed resist, while leaving unexposed resist unaffected. In our system the size of the rectangular beam spot is programmably defined by two L-shaped tantalum blades with well-polished edges. This allows rapid exposure of entire rectangular pattern elements up to 500 × 500 μm in one step. By combin…

Development of an MeV ion beam lithography system in Jyväskylä

Abstract A lithographic facility for writing patterns with ion beams from cyclotron beams is under development for the Jyvaskyla cyclotron. Instead of focusing and deflecting the beam with electrostatic and magnetic fields a different approach is used. Here a small rectangular beam spot is defined by the shadow of a computer-controlled variable aperture in close proximity to the sample. This allows parallel exposure of rectangular pattern elements of 5–500 μm side with protons up to 6 MeV and heavy ions (20Ne, 85Kr) up to few 100 MeV. Here we present a short overview of the system under construction and development of the aperture design, which is a critical aspect for all ion beam lithogra…

Nano-imaging of single cells using STIM

Scanning transmission ion microscopy (STIM) is a technique which utilizes the energy loss of high energy (MeV) ions passing through a sample to provide structural images. In this paper, we have successfully demonstrated STIM imaging of single cells at the nano-level using the high resolution capability of the proton beam writing facility at the Centre for Ion Beam Applications, National University of Singapore. MCF-7 breast cancer cells (American Type Culture Collection [ATCC]) were seeded on to silicon nitride windows, backed by a Hamamatsu pin diode acting as a particle detector. A reasonable contrast was obtained using 1 MeV protons and excellent contrast obtained using 1 MeV alpha parti…

Development of micro-contact printing of osteosarcoma cells using MeV ion beam lithography

Abstract For investigation of spatial effects in signalling between cells and also signal substances that trigger cell proliferation and behaviour we are developing a micro Contact Printing process ( μ CP ) . In order to allow printing of cells stamps with high aspect ratio are required and these have been fabricated using Programmed Proximity Aperture Lithography (PPAL) with 3 MeV 4 He 2 + ions to produce PMMA masters for casting the stamps in PDMS. A simple printing device was developed and the first results using this to print human osteosarcoma cells is demonstrated.

Resolution performance of programmable proximity aperture MeV ion beam lithography system

AbstractAn ion beam lithography system for light and heavy ions has been developed at the University of Jyväskylä's Accelerator Laboratory. The system employs a programmable proximity aperture to define the beam. The proximity aperture is made up of four Ta blades with precise straight edges that cut the beam in the horizontal and vertical directions. The blade positions and dimensions are controlled by a pair of high-precision linear-motion positioners. The sample is mounted on a X-Y-Z stage capable of moving with 100 nm precision steps under computer control. The resolution performance of the system is primarily governed by the proximity aperture. Pattern edge sharpness is set by the beam…

Crystallographic analysis of extended defects in diamond-type crystals

Abstract To investigate irradiation-induced Si amorphization during its initial stages, we have performed a classical molecular-dynamics (MD) calculation for the case of self-irradiation by 5 keV ions at a low temperature of 100 K. We examined the geometry of self-interstitial atom (SIA) clusters using the pixel mapping (PM) method, on the output data of MD calculations. Perfect crystalline silicon (c-Si) is amorphized by self-irradiation, and we observe that many SIA are produced. During sequential self-irradiation, the most frequently observed species were isolated SIA, i.e. I1 (monomer). The fractions of SIA clusters decreased as I2 (dimer), I3 (trimer), and I4 (tetramer) clusters, respe…

Detection of planar defects caused by ion irradiation in Si using molecular dynamics

We have analyzed the evolution of defects caused by self-irradiation of crystalline silicon. A classical molecular dynamics simulation was followed by defect analysis using the Pixel Mapping (PM) method. The PM identified {311} planar defects and long-chain structures of the so-called interstitial chains following low energy (1 keV) ion impact. The areal density obtained from simulation of self-interstitial atoms was about two thirds of that of experiments reported in the literature [Jpn. J. Appl. Phys. 30 (1991) L639], while the atomic configuration on respective planes agreed exactly.

Basics of Ion Scattering in Nanoscale Materials

Energetic ions interact with materials by collisions with the nuclei and electrons of the atoms that make up the material. In these collisions, energy and momentum is transferred from the projectile particle, which is a moving atom or ion, to the target particles (atomic nucleus or electron). Each collision leads to a slowing down of the moving projectile and also a deflection of the trajectory that gives rise to the term scattering, which is often used synonymously to describe the energy transfer process.

Development of economic MeV-ion microbeam technology at Chiang Mai University

Abstract Developing high technologies but in economic manners is necessary and also feasible for developing countries. At Chiang Mai University, Thailand, we have developed MeV-ion microbeam technology based on a 1.7-MV Tandetron tandem accelerator with our limited resources in a cost-effective manner. Instead of using expensive and technically complex electrostatic or magnetic quadrupole focusing lens systems, we have developed cheap MeV-ion microbeams using programmed L-shaped blade aperture and capillary techniques for MeV ion beam lithography or writing and mapping. The programmed L-shaped blade micro-aperture system consists of a pair of L-shaped movable aperture pieces which are contr…

Characterisation of beam focus quality in biomedical nuclear microscopy: A Fourier optics approach

Abstract The central peak widths of the 2D-autocorrelation function have been investigated as a Figure of Merit (FoM) of focus quality in nuclear microscopy using a quadrupole triplet lens system. The beam focus could be reliably characterised for direct scanning transmission ion microscopy (direct-STIM) images obtained with fluences as small as 5.8 × 10 9 ions cm - 2 which colocalisation tests showed did not introduce significant beam-induced changes in the cells.

Proton beam written hydrogen silsesquioxane (HSQ) nanostructures for Nickel electroplating

Abstract Hydrogen silsesquioxane (HSQ) behaves as a negative resist under MeV proton beam exposure. HSQ is a high-resolution resist suitable for production of tall ( 1.5 μ m ) high-aspect-ratio nanostructures with dimensions down to 22 nm. High-aspect-ratio HSQ structures are required in many applications, e.g. nanofluidics, biomedical research, etc. Since P-beam writing is a direct and hence slow process, it is beneficiary to fabricate a reverse image of the patterns in a metallic stamp, e.g. by Ni electroplating. The Ni stamp can then be used to produce multiple copies of the same pattern. In this study we investigate the possibility to produce Ni stamps from p-beam written HSQ samples. H…

Growth of osteoblasts on lithographically modified surfaces

Here we report about preliminary investigations on developing substrates for culturing osteoblasts, the cells responsible for production of mineralised bone, by lithographically modifying the surfaces of several materials. The proton beam writing system at the National University of Singapore was used to fabricate high aspect ratio structures in PMMA, while two-dimensional low aspect ratio structures were fabricated using conventional electron beam lithography (EBL) and UV lithography (UVL) in SU-8. It was found that oxygen plasma treatment of structured SU-8 surfaces changed the surface layer and significantly improved cell attachment and proliferation. Cells grown on patterned thick PMMA …

Low-energy primary knock on atom damage distributions near MeV proton beams focused to nanometre dimensions

Abstract In this preliminary study, the spatial extent of the defects introduced in Si by a normally incident 1 MeV H + nanobeam was investigated using a hybrid approach. First, the standard SRIM code was employed to calculate the angular and energy distributions of Primary Knock-on Atoms (PKA) using the Binary Collision Approximation (BCA). The long mean free path and the kinematics of scattering in a screened Coulomb potential resulted in an anisotropic PKA distribution that was mainly directed perpendicular to the primary ion trajectories. The PKA energy E dependence was close to 1/ E n with 1.5  n The results revealed that the low energy PKA’s resulted in localised damaged regions with …

Programmable proximity aperture lithography with MeV ion beams

A novel MeV ion beam programmable proximity aperture lithography system has been constructed at the Accelerator Laboratory of the University of Jyvaskyla, Finland. This facility can be used to fabricate three dimensional microstructures in thick (<100μm) polymer resist such as polymethylmethacrylate. In this method, MeV ion beams from the 1.7 MV pelletron and K130 cyclotron accelerators are collimated to a beam spot of rectangular shape. This shape is defined by a computer-controlled aperture made of a pair of L-shaped Ta blades which are in close proximity to the sample to minimize the penumbra broadening. Here the authors report on development of the system, the controlling software, the …

Aperture-edge scattering in MeV ion-beam lithography. II. Scattering from a rectangular aperture

The capability of collimators to define beams of MeV ions with sub-100nm dimensions has recently been demonstrated. Such nanometer beams have potential applications in MeV ion-beam lithography, which is the only maskless technique capable of producing extremely high aspect-ratio micro- and nanostructrures, as well as in high resolution MeV ion-beam imaging. Ion scattering from the collimator edges can be a resolution-restricting factor in these applications. Scattering processes at edges are difficult to study using conventional simulation codes because of the complicated geometry. In this part of our work, the authors used the GEANT4 toolkit as a simulation tool for studying the behavior o…

Angular spreading measurements using MeV ion microscopes

Abstract The sharpness of MeV ion microscope images is governed by small-angle scattering and associated lateral spreading of the ion beam in the sample. We have investigated measurement of the half-angle of the angular spreading distribution by characterising the image blurring in direct-Scanning Transmission Ion Microscopy (direct-STIM). In these tests Mylar™ foils of 0.5–6 μm were used to induce angular spreading. Images were taken of an electron microscope grid using 2 MeV protons with, and without, the foils in the beam path. The blurring was measured by fitting the width of a circular Gaussian point spread function to the images with and without the foil in position. The results show …

Ion-induced fluorescence imaging of endosomes

Abstract Imaging laboratories at Jyvaskyla and Singapore are collaborating on the development of fluorescence imaging of cytoplasmic endosomes using a combination of proton induced fluorescence (PIF) with direct Scanning Transmission Ion Microscopy (direct-STIM) for sub-cellular structural imaging. A549 lung carcinoma cells were cultivated and stained for epidermal growth factor receptor (EGFR) and receptor α2β1 integrin. In this paper, we demonstrate that cells can be imaged at sub-150 nm resolution using the PIF technique. In addition, the same target cell was imaged at 50 and 25 nm resolution by using proton and He-STIM, respectively. The combination of both techniques offer a powerful t…

Aperture edge scattering in focused MeV ion beam lithography and nuclear microscopy: An application for the GEANT4 toolkit

Collimators are widely used to define MeV ion beams. Recent studies have shown the capability of combinations of collimators and lenses to define beams of MeV ions with sub-100 nanometre dimensions. Such nanometre beams have potential applications in MeV ion beam lithography, which is the only maskless technique capable of producing extremely high aspect ratio micro- and nano-structrures, as well as in high resolution MeV ion beam based imaging. The ion scattering from the collimator-edges can be a resolution restricting factor in these applications. Scattering processes at edges are difficult to study using conventional simulation codes because of the complicated geometry. In this work we …

Development of a microfluidic design for an automatic lab-on-chip operation

Simple and easy to use are the keys for developing lab-on-chip technology. Here, a new microfluidic circuit has been designed for an automatic lab-on-chip operation (ALOCO) device. This chip used capillary forces for controlled and precise manipulation of liquids, which were loaded in sequence from different flowing directions towards the analysis area. Using the ALOCO design, a non-expert user is able to operate the chip by pipetting liquids into suitable inlet reservoirs. To test this design, microfluidic devices were fabricated using the programmable proximity aperture lithography technique. The operation of the ALOCO chip was characterized from the flow of red-, blue- and un-dyed deioni…

MeV ion beam lithography of biocompatible halogenated Parylenes using aperture masks

Parylenes are poly(p-xylylene) polymers that are widely used as moisture barriers and in biomedicine because of their good biocompatibility. We have investigated MeV ion beam lithography using 16O+ ions for writing defined patterns in Parylene-C, which is evaluated as a coating material for the Cochlear Implant (CI) electrode array, a neuroprosthesis to treat some forms of deafness. Parylene-C and -F on silicon and glass substrates as well as 50 μm thick PTFE were irradiated to different fluences (1×1013-1×10161×1013-1×1016 1 MeV 16O+ ions cm−2) through aperture masks under high vacuum and a low pressure (&lt;10−3 mbar) oxygen atmosphere. Biocompatibility of the irradiated and unirradiated …

Transport of Water and Particles in Microfluidics Devices Lithographically Fabricated Using Proton Beam Writing (PBW)

Proton beam writing (PBW) is a MeV ion beam lithography technique that has gained interest in many biological applications such as fabricating microfluidic devices for Lab-On-a-Chip (LOC) applications where capillary forces are important for fluid flow. PBW has a unique capability of being able to direct-write patterns in thick (1-30µm) polymer resist layers with straight vertical sidewalls. It can be used to prepare master stamps and moulds for mass production in polymeric materials. A recent development, where the direct writing of an entire pattern element is carried out in parallel makes PBW especially well suited for Bio-MEMS LOC applications. In this study we have examined the flow dy…

Depth profiling of Al2O3 + TiO2 nanolaminates by means of a time-of-flight energy spectrometer

Atomic layer deposition (ALD) is currently a widespread method to grow conformal thin films with a sub-nm thickness control. By using ALD for nanolaminate oxides, it is possible to fine tune the electrical, optical and mechanical properties of thin films. In this study the elemental depth profiles and surface roughnesses were determined for Al2O3 + TiO2 nanolaminates with nominal single-layer thicknesses of 1, 2, 5, 10 and 20 nm and total thickness between 40 nm and 60 nm. The depth profiles were measured by means of a time-of-flight elastic recoil detection analysis (ToF-ERDA) spectrometer recently installed at the University of Jyväskylä. In TOF-E measurements 63Cu, 35Cl, 12C and 4He ions…

Fabrication of a negative PMMA master mold for soft-lithography by MeV ion beam lithography

Abstract In this study, poly(methyl methacrylate) (PMMA) was investigated as a negative resist by irradiation with a high-fluence 2 MeV proton beam. The beam from a 1.7 MV Tandetron accelerator at the Plasma and Beam Physics Research Facility (PBP) of Chiang Mai University is shaped by a pair of computer-controlled L-shaped apertures which are used to expose rectangular pattern elements with 1–1000 μm side length. Repeated exposure of rectangular pattern elements allows a complex pattern to be built up. After subsequent development, the negative PMMA microstructure was used as a master mold for casting poly(dimethylsiloxane) (PDMS) following a standard soft-lithography process. The PDMS chi…

Lithography exposure characteristics of poly(methyl methacrylate) (PMMA) for carbon, helium and hydrogen ions

Abstract Poly(methyl methacrylate) is a common polymer used as a lithographic resist for all forms of particle (photon, ion and electron) beam writing. Faithful lithographic reproduction requires that the exposure dose, Θ, lies in the window Θ 0 ⩽ Θ Θ × 0 , where Θ 0 and Θ × 0 represent the clearing and cross-linking onset doses, respectively. In this work we have used the programmable proximity aperture ion beam lithography systems in Chiang Mai and Jyvaskyla to determine the exposure characteristics in terms of fluence for 2 MeV protons, 3 MeV 4 He 2 + and 6 MeV 12 C 3 + ions, respectively. After exposure the samples were developed in 7:3 by volume propan-2-ol:de-ionised water mixture. At…

Angular and lateral spreading of ion beams in biomedical nuclear microscopy

Abstract Nuclear scattering from target atoms gives rise to a spatial broadening of energetic ion beams penetrating matter. The spatial broadening of the ion beam presents an ultimate limit to the resolving power that can be achieved in nuclear microscopy methods. The pressing of the attainable resolution limit in biomedical nuclear microscopy to dimensions approaching 10 nm, or so, implies the fundamental limitation from ion-target scattering will become increasingly significant. This effect has been investigated by a combined analytical and numerical computational approach to determine the extent and how single and multiple scattering processes limit the resolution for analysis with 2 MeV…