1,124 research outputs found

    Determination of 2D implanted ion distributions using inverse radon transform methods

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    Two methods are presented for the experimental determination of 2D implanted ion distribution resulting from implantations with a line source into amorphous targets. It is shown that the relation between the 2D distribution and the depth profiles resulting from tilted angle implantations is described by the Radon transformation. The inverse transformation has been applied to accurately measured depth profiles. The first method uses a digitization of the 2D distribution and the second method uses a parameterized function for the 2D distribution. The methods are tested for a 400 keV boron implantation in an amorphous layer of silicon. The experimental obtained 2D distributions are compared with a TRIM Monte Carlo simulation. A good agreement between experiment and simulation is observed

    Ion beam processing of surfaces and interfaces – Modeling and atomistic simulations

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    Self-organization of regular surface pattern under ion beam erosion was described in detail by Navez in 1962. Several years later in 1986 Bradley and Harper (BH) published the first self-consistent theory on this phenomenon based on the competition of surface roughening described by Sigmund’s sputter theory and surface smoothing by Mullins-Herring diffusion. Many papers that followed BH theory introduced other processes responsible for the surface patterning e.g. viscous flow, redeposition, phase separation, preferential sputtering, etc. The present understanding is still not sufficient to specify the dominant driving forces responsible for self-organization. 3D atomistic simulations can improve the understanding by reproducing the pattern formation with the detailed microscopic description of the driving forces. 2D simulations published so far can contribute to this understanding only partially. A novel program package for 3D atomistic simulations called trider (TRansport of Ions in matter with DEfect Relaxation), which unifies full collision cascade simulation with atomistic relaxation processes, has been developed. The collision cascades are provided by simulations based on the Binary Collision Approximation, and the relaxation processes are simulated with the 3D lattice kinetic Monte-Carlo method. This allows, without any phenomenological model, a full 3D atomistic description on experimental spatiotemporal scales. Recently discussed new mechanisms of surface patterning like ballistic mass drift or the dependence of the local morphology on sputtering yield are inherently included in our atomistic approach. The atomistic 3D simulations do not depend so much on experimental assumptions like reported 2D simulations or continuum theories. The 3D computer experiments can even be considered as ’cleanest’ possible experiments for checking continuum theories. This work aims mainly at the methodology of a novel atomistic approach, showing that: (i) In general, sputtering is not the dominant driving force responsible for the ripple formation. Processes like bulk and surface defect kinetics dominate the surface morphology evolution. Only at grazing incidence the sputtering has been found to be a direct cause of the ripple formation. Bradley and Harper theory fails in explaining the ripple dynamics because it is based on the second-order-effect ‘sputtering’. However, taking into account the new mechanisms, a ‘Bradley-Harper equation’ with redefined parameters can be derived, which describes pattern formation satisfactorily. (ii) Kinetics of (bulk) defects has been revealed as the dominating driving force of pattern formation. Constantly created defects within the collision cascade, are responsible for local surface topography fluctuation and cause surface mass currents. The mass currents smooth the surface at normal and close to normal ion incidence angles, while ripples appear first at θ ≥ 40°. The evolution of bimetallic interfaces under ion irradiation is another application of trider described in this thesis. The collisional mixing is in competition with diffusion and phase separation. The irradiation with He+ ions is studied for two extreme cases of bimetals: (i) Irradiation of interfaces formed by immiscible elements, here Al and Pb. Ballistic interface mixing is accompanied by phase separation. Al and Pb nanoclusters show a self-ordering (banding) parallel to the interface. (ii) Irradiation of interfaces by intermetallics forming species, here Pt and Co. Well-ordered layers of phases of intermetallics appear in the sequence Pt/Pt3Co/PtCo/PtCo3/Co. The trider program package has been proven to be an appropriate technique providing a complete picture of mixing mechanisms

    Shape Evolution of Nanostructures by Thermal and Ion Beam Processing: Modeling & Atomistic Simulations

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    Single-crystalline nanostructures often exhibit gradients of surface (and/or interface) curvature that emerge from fabrication and growth processes or from thermal fluctuations. Thus, the system-inherent capillary force can initiate morphological transformations during further processing steps or during operation at elevated temperature. Therefore and because of the ongoing miniaturization of functional structures which causes a general rise in surface-to-volume ratios, solid-state capillary phenomena will become increasingly important: On the one hand diffusion-mediated capillary processes can be of practical use in view of non-conventional nanostructure fabrication methods based on self-organization mechanisms, on the other hand they can destroy the integrity of nanostructures which can go along with the failure of functionality. Additionally, capillarity-induced shape transformations are effected and can thereby be controlled by applied fields and forces (guided or driven evolution). With these prospects and challenges at hand, formation and shape transformation of single-crystalline nanostructures due to the system-inherent capillary force in combination with external fields or forces are investigated in the frame of this dissertation by means of atomistic computer simulations. For the exploration (search, description, and prediction) of reaction pathways of nanostructure shape transformations, kinetic Monte Carlo (KMC) simulations are the method of choice. Since the employed KMC code is founded on a cellular automaton principle, the spatio-temporal development of lattice-based N-particle systems (N up to several million) can be followed for time spans of several orders of magnitude, while considering local phenomena due to atomic-scale effects like diffusion, nucleation, dissociation, or ballistic displacements. In this work, the main emphasis is put on nanostructures which have a cylindrical geometry, for example, nanowires (NWs), nanorods, nanotubes etc

    A Monte Carlo simulation of the Sudbury Neutrino Observatory proportional counters

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    The third phase of the Sudbury Neutrino Observatory (SNO) experiment added an array of 3He proportional counters to the detector. The purpose of this Neutral Current Detection (NCD) array was to observe neutrons resulting from neutral-current solar neutrino-deuteron interactions. We have developed a detailed simulation of the current pulses from the NCD array proportional counters, from the primary neutron capture on 3He through the NCD array signal-processing electronics. This NCD array Monte Carlo simulation was used to model the alpha-decay background in SNO's third-phase 8B solar-neutrino measurement.Comment: 38 pages; submitted to the New Journal of Physic

    Effects of implementation of decaborane ions in silicon

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    The next generations of Si microelectronic devices will require ultra shallow p-type junctions formed by implantation of B ions with energies below 1 keV, at which available beam currents are severely limited by space charge effects. To solve this problem, decaborane (B10H14) cluster ion implantation has been suggested as an attractive alternative to conventional B implants, because one decaborane ion implants ten B atoms simultaneously and each of the B atoms only carries approximately 1/11 of the total ion energy. Thus the same implantation depth and dose as with monomer B ions can be obtained using decaborane ions but with 10 times less charge and ten times higher energy. In this dissertation research, various effects of implantation of decaborane cluster ions in silicon were studied, using an experimental ion implanter in the Ion Beam and Thin Film Research Laboratory at NJIT. Secondary Ion Mass Spectrometry (SIMS) depth profiles of boron and hydrogen in decaborane-implanted samples were measured before and after thermal activation annealing and compared to that in the control samples. Shallow p-type junction could be achieved with decaborane implantation. The co-implanted hydrogen diffused out almost entirely after annealing and hence is expected to have a negligible effect on the device performance. Transient enhanced diffusion (TED) of B atoms in Si implanted with mass analyzed decaborane ions of three energies were measured and compared to that of B atoms in Si implanted with B+ ions of equivalent B energy and dose. The resultsdemonstrated that implantation of B with decaborane cluster ions led to essentially the same amount of TED of B in Si as that in Si implanted with atomic B+ ions of the equivalent energy and dose. The sputtering yields of Si with B in the form of decaborane clusters were measured and compared to those for boron monomer ions, estimated using an empirical formula. The surface morphology of amorphous Si, crystalline Si and Ta film irradiated with energetic decaborane ions and argon ions were studied using Atomic Force Microscopy (AFM). Results of surface roughness and Power Spectral Density (PSD) analysis show that decaborane cluster ions smooth rather than roughen these surfaces. Molecular Dynamics (MD) simulations have been performed to compare impact effects on Si target by B monomers and B10 clusters at the same energy per B atom. B depth profiles were found to be similar for B atoms implanted with B10 clusters and with B monomers. The crater formation, a unique feature of cluster impacts, was also observed on the Si surface impacted by a B10 cluster. The calculated sputtering yield of Si (the number of ejected Si atoms per incident B) was much larger with B10 clusters than with B monomers and also larger than the experimental values. The results of this research confirm that decaborane implantation is a viable alternative to low energy B implantation for ultra shallow p-type junction formation. These results also contribute to the knowledge base of the technology of ultra shallow B doping in CMOS devices and will help to better understand cluster-solid interactions in general

    Advanced Focused Beam-Induced Processing for Nanoscale Synthesis and 2D Materials Device Architectures

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    Nanofabrication has come to prominence over recent years due to miniaturization of electronic devices as well as interesting physical phenomena that arise in material systems at the nanoscale. Particle beam induced processing enables additive as well as subtractive nanoprocessing techniques. Focused beam induced processing facilitates direct-write processing, thus making it a common technique for fabrication and synthesis on the nanoscale and is typically carried out with charged particles such as electrons or ion species, each of which offer distinct capabilities. This dissertation addresses several challenges which currently plague the focused beam-induced processing community and explores novel applications.Chapter I explores laser based purification strategies for electron beam induced deposition. This addresses the challenge of material purity, which currently limits broader application of the nanofabrication technique. Chapter II covers advanced helium ion beam induced processing using a Gas Field Ionization source. This chapter explores novel applications for the helium ion beam as well as the mitigation of helium-induced subsurface damage, which currently prevents ubiquitous adoption of the helium ion microscope as a nanofabrication tool. Chapter III studies defect introduction in 2D materials under helium ion irradiation, which proves to be an ideal nanoprocessing application for the helium ion beam

    Reactive ion beam figuring of optical aluminium surfaces

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    Ultra-smooth and arbitrarily shaped reflective optics are necessary for further progress in EUV/XUV lithography, x-ray and synchrotron technology. As one of the most important technological mirror optic materials, aluminium behaves in a rather difficult way in ultra-precision machining with such standard techniques as diamond-turning and subsequent ion beam figuring (IBF). In particular, in the latter, a strong surface roughening is obtained. Hence, up to now it has not been possible to attain the surface qualities required for UV or just visible spectral range applications. To overcome the limitations mainly caused by the aluminium alloy structural and compositional conditions, a reactive ion beam machining process using oxygen process gas is evaluated. To clarify the principle differences in the effect of oxygen gas contrary to oxygen ions on aluminium surface machining, we firstly focus on chemical-assisted ion beam etching (CAIBE) and reactive ion beam etching (RIBE) experiments in a phenomenological manner. Then, the optimum process route will be explored within a more quantitative analysis applying the concept of power spectral density (PSD) for a sophisticated treatment of the surface topography. Eventually, the surface composition is examined by means of dynamic secondary ion mass spectrometry (SIMS) suggesting a characteristic model scheme for the chemical modification of the aluminium surface during oxygen ion beam machining. Monte Carlo simulations were applied to achieve a more detailed process conception
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