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

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

IM3D: A parallel Monte Carlo code for efficient simulations of primary radiation displacements and damage in 3D geometry

SRIM-like codes have limitations in describing general 3D geometries, for modeling radiation displacements and damage in nanostructured materials. A universal, computationally efficient and massively parallel 3D Monte Carlo code, IM3D, has been developed with excellent parallel scaling performance. IM3D is based on fast indexing of scattering integrals and the SRIM stopping power database, and allows the user a choice of Constructive Solid Geometry (CSG) or Finite Element Triangle Mesh (FETM) method for constructing 3D shapes and microstructures. For 2D films and multilayers, IM3D perfectly reproduces SRIM results, and can be ∼10[superscript 2] times faster in serial execution and > 10[superscript 4] times faster using parallel computation. For 3D problems, it provides a fast approach for analyzing the spatial distributions of primary displacements and defect generation under ion irradiation. Herein we also provide a detailed discussion of our open-source collision cascade physics engine, revealing the true meaning and limitations of the “Quick Kinchin-Pease” and “Full Cascades” options. The issues of femtosecond to picosecond timescales in defining displacement versus damage, the limitation of the displacements per atom (DPA) unit in quantifying radiation damage (such as inadequacy in quantifying degree of chemical mixing), are discussed.National Natural Science Foundation (China) (Grant 11275229)National Natural Science Foundation (China) (Grant 11475215)National Natural Science Foundation (China) (Grant NSAF U1230202)National Natural Science Foundation (China) (Grant 11534012)National Basic Research Program of China (973 Program) (Grant 2012CB933702)Hefei Center for Physical Science and Technology (Grant 2012FXZY004)Chinese Academy of Sciences (Hefei Institutes of Physical Science (CASHIPS) Director Grant)National Science Foundation (U.S.) (DMR-1410636)National Science Foundation (U.S.) (DMR-1120901

Improved physical models for advanced silicon device processing

Producción CientíficaWe review atomistic modeling approaches for issues related to ion implantation and annealing in advanced device processing. We describe how models have been upgraded to capture physical mechanisms in more detail as a response to the accuracy demanded in modern process and device modeling. Implantation and damage models based on the binary collision approximation have been improved to describe the direct formation of amorphous pockets for heavy or molecular ions. The use of amorphizing implants followed by solid phase epitaxial regrowth has motivated the development of detailed models that account for amorphization and recrystallization, considering the influence of crystal orientation and stress conditions. We apply simulations to describe the role of implant parameters to minimize residual damage, and we address doping issues that arise in non-planar structures such as FinFETs.Ministerio de Ciencia e Innovación - FEDER (Proyect TEC2014-60694-P)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA331U14

A review of spacecraft material sputtering by Hall thruster plumes

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76408/1/AIAA-2001-3353-473.pd

Atomistic simulations of plasma-material interactions in fusion reactors

With increasing demand for the energy in last decades, replacing scarce fossil fuels with new energy resources is inevitable. Currently, there is no clear alternative to the old and regular energy production methods for a clean future. However, nuclear fusion power may offer practical, power-plant-scale energy production with an unlimited fuel supply. A major challenge to overcome in the fusion reaction is to produce more energy than it consumes under extremely harsh operating conditions. In the last few decades, a wide range of studies have been carried out to investigate fusion performance and fusion reactor designs. ITER will be the first experimental tokamak-like nuclear fusion reactor to produce net energy, based on deuterium–tritium plasma. Due to the ITER design and operation requirements, extreme conditions are expected for plasma-facing components, such as very large thermal loads, temperature and particle fluxes. Therefore, selecting appropriate materials for different components of the device is critical and highly demanding. The main candidates for the first wall materials in future fusion reactor, ITER are tungsten for the divertor plates and beryllium for the main wall. Moreover, special low-activation ferritic steels are developed for being used as structural materials in blanket modules. In addition, various steels containing of iron and carbon are being considered for the main wall of the DEMO. The plasma cannot be confined infinitely and to control the contact between the escaped plasma and the wall, the area of interaction is restricted to divertor or limiter structures, leading to erosion of them. This phenomenon can become a show stopper by limiting the lifetime of wall materials. Therefore, characterizing the erosion behavior and morphology changes of these components and understanding the underlying mechanism are essential toward predicting and ultimately controlling the adverse effects of plasma surface interactions. Experiments in the different tokamaks and linear plasma devices, as well as those using ion beams are dedicated to study plasma surface interactions. However, experiments show a complex outcome and provide insufficient information to understand the underlying mechanism if the physics is poorly understood. In addition to experiments, computer simulations to study plasma surface interaction have also contributed to a better understanding of future fusion reactors and characterization of this mechanism in a wide range of time and length scales. In this dissertation, the plasma wall interactions such as erosion and ion reflection for the firstwall materials of future fusion reactors have been studied by different computational methods. The interactions of different materials with plasma and impurity particles were modelled. The work was mainly based on molecular dynamics (MD) simulations and an Object Kinetic Monte Carlo (OKMC) algorithm to extend earlier results to a longer time and length scales and thereby enables direct comparison with performed experiments. First, deuterium irradiation on pure Fe, Fe with 1% C impurity and Fe 3 C, under different irradiation energies and substrate temperatures was modelled. Furthermore, a MD study to investigate the effect of plasma impurities D, Ar and Ne on the erosion and surface structure of W and Be was carried out for different fractions of Ar and Ne. Furthermore, the effect of reactor-relevant parameters on Be erosion behaviour and surface changes have been investigated using MD and subsequently a multi-scale approach (KMC- MD).Energian lisääntyvä kysyntä viime vuosikymmeninä on väistämätöntä vähentää niukkoja fossiilisia polttoaineita uusilla energiaresursseilla. Tällä hetkellä ei ole selkeää vaihtoehtoa puhtaiden tulevaisuuden vanhojen ja säännöllisten energiantuotantomenetelmien kannalta. Kuitenkin ydinfuusioteho voi tarjota käytännöllistä, voimalaitosten energiatehokkuutta ja rajoittamatonta polttoainevarastoa. Suuri haaste voittamaan fuusioreaktiossa on tuottaa enemmän energiaa kuin kuluttaa äärimmäisen vaikeissa käyttöolosuhteissa. Viime vuosikymmeninä on suoritettu laaja valikoima tutkimuksia fuusio- ja fuusioreaktoreiden tutkimiseksi. ITER on ensimmäinen kokeellinen tokamak-kaltainen ydinfuusioreaktori, joka tuottaa nettoenergian, joka perustuu deuterium-tritium-plasmaan. ITERin suunnittelu- ja käyttövaatimusten vuoksi odotetaan äärimmäisiä olosuhteita plasmapinnoittaville komponenteille, kuten erittäin suurille lämpökuormituksille, lämpötiloille ja hiukkasvirtauksille. Sen vuoksi sopivan materiaalin valitseminen laitteen eri osiin on kriittinen ja erittäin vaativa. Tulevan fuusioreaktorin, ITERin, ensimmäisen seinämateriaalin tärkeimmät ehdokkaat ovat volframia pääseinämän taustalevyille ja berylliumille. Lisäksi kehitetään erityisiä alhaisen aktivoinnin omaavia ferriittisiä teräksiä, joita käytetään rakenteellisina materiaalina peitemoduulissa. Lisäksi DEMO: n pääseinässä harkitaan erilaisia ​​teräksisiä rautaa ja hiiltä sisältäviä teräksiä. Plasmaa ei voida rajata äärettömän rajoitetusti ja kontrolloida karkaistun plasman ja seinän välistä kosketusta, vuorovaikutusalue rajoitetaan hajautus- tai rajoittimen rakenteisiin, mikä johtaa niiden eroosioon. Tämä ilmiö voi tulla näyttäytymään rajoittamalla seinäaineiden käyttöikää. Siksi näiden komponenttien eroosiokäyttäytymisen ja morfologian muutosten karakterisointi ja taustalla olevan mekanismin ymmärtäminen ovat välttämättömiä plasman pinnan vuorovaikutusten ennustamisen ja lopulta torjumiseksi. Kokeita erilaisissa tokamaakseissa ja lineaarisissa plasmasuihkulaitteissa sekä ionisäteitä käyttävissä kiteissä on sitoutunut tutkimaan plasman pinnan vuorovaikutuksia. Kokeet osoittavat kuitenkin monimutkaisia ​​tuloksia ja tarjoavat riittämättömät tiedot ymmärtämään taustalla olevaa mekanismia, jos fysiikka on huonosti ymmärretty. Kokeiden lisäksi tietokoneiden simulaatiot plasman pinnan vuorovaikutuksen tutkimiseksi ovat osaltaan lisänneet tulevien fuusioreaktorien ymmärrystä ja tämän mekanismin karakterisointia monissa aikapituus- ja pituusasteissa. Tässä väitöskirjassa on tutkittu plasman seinän vuorovaikutuksia, kuten tulevien fuusioreaktorien ensimmäisen seinämateriaalin eroosiota ja ionin heijastusta erilaisilla laskennallisilla menetelmillä. Eri materiaalien vuorovaikutukset plasman ja epäpuhtauspartikkeleiden kanssa mallinnettiin. Työssä keskityttiin pääasiassa molekyylidynamiikan (MD) simulaatioiden ja Object Kinetic Monte Carlo (OKMC) -algoritmien avulla aikaisempiin tuloksiin pitemmän ajan ja pituuden mittakaavaksi ja siten suoran vertailun suoritetuista kokeista. Ensinnäkin mallinnettiin deuterium säteilytys puhtaalla Fe: llä, Fe: llä 1% C: n epäpuhtaudella ja Fe 3 C: lla eri säteilytysenergioilla ja substraattilämpötiloilla. Lisäksi Ar: n ja Ne: n eri fraktioille suoritettiin MD-tutkimus plasman epäpuhtauksien D, Ar ja Ne vaikutuksen selvittämiseksi W: n ja Be: n eroosion ja pintarakenteen suhteen. Lisäksi reaktoriin liittyvien parametrien vaikutus BE: n eroosionkäyttäytymiseen ja pinnan muutoksiin on tutkittu käyttäen MD: tä ja sen jälkeen monimuotoista lähestymistapaa (KMC-MD)

Development of Hybrid Deterministic-Statistical Models for Irradiation Influenced Microstructural Evolution.

Ion irradiation holds promise as a cost-effective approach to developing structured nano--porous and nano--fiberous semiconductors. Irradiation of certain semiconductors leads to the development of these structures, with exception of the much desired silicon. Hybrid deterministic-statistical models were developed to better understand the dominating mechanisms during structuring. This dissertation focuses on the application of hybrid models to two different radiation damage behavior: (1) precipitate evolution in a binary two-phase system and (2) void nucleation induced nano--porous structuring. Phenomenological equations defining the deterministic behavior were formulated by considering the expected kinetic and phenomenological behavior. The statistical component of the models is based on the Potts Monte Carlo (PMC) method. It has been demonstrated that hybrid models efficiently simulate microstructural evolution, while retaining the correct kinetics and physics. The main achievement was the development of computational methods to simulate radiation induced microstructural evolution and highlight which processes and materials properties could be essential for nano--structuring. Radiation influenced precipitate evolution was modeled by coupling a set of non-linear partial differential equations to the PMC model. The simulations considered the effects of dose rate and interfacial energy. Precipitate growth becomes retarded with increased damage due to diffusion of the radiation defects countering capillarity driven precipitate growth. The effects of grain boundaries (GB) as sinks was studied by simulating precipitate growth in an irradiated bi-crystalline matrix. Qualitative comparison to experimental results suggest that precipitate coverage of the GB is due to kinetic considerations and increased interfacial energy effects. Void nucleation induced nano--porous/fiberous structuring was modeled by coupling rate theory equations, kinetic Monte Carlo swelling algorithm and the PMC model. Point defect (PD) diffusivities were parameterized to study their influence on nano--structuring. The model showed that PD kinetic considerations are able to describe the formation of nano--porous structures. As defects diffuse faster, void nucleation becomes limited due to the fast removal of the defects. It was shown that as the diffusivities' ratio diverges from unity, the microstructures become statistically similar and uniform. Consequently, the computational results suggest that nano--pore structuring require interstitials that are much faster than the slow diffusing vacancies, which accumulate and cluster into voids.PhDNuclear Engineering and Radiological SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111424/1/efrainhr_1.pd