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003.01. NATIONAL LABORATORY ASTANA

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Open Access
The clusters growth and evaporation rate constante calculation by using of molecular dynamics method for condensation behind the shock front
(Matem. Mod., 1993) Insepov, Z.; Karatajev, E. M.
Molecular dynamics model of calculation of the growth and evaporation rate constants of dusters is proposed. Calculations for small clusters are carried out. On the basis of the chemical mechanism the characteristic time of condensation is achieved, which is in available agreement with experiment on condensation of iron vapors behind the shock front.
Open Access
Molecular-dynamics simulation of thin-film growth by energetic cluster impact
(Physical Review B, 1995) Haberland, H.; Insepov, Z.; Moseler, M.
Langevin-molecular-dynamics simulations of thin-film growth by energetic cluster impact were carried out. The impact of a Mo 1043 cluster on a Mo(001) surface was studied for impact energies of 0.1, 1, and 10 eV/atom using the Finnis-Sinclair many-body potential. The characteristics of the collision range from a soft touchdown at 0.1 eV/atom, over a flattening collision at 1 eV/atom, to a meteoric impact at 10 eV/atom. The highest energy impact creates a pressure of about 100 GPa in the impact zone and sends a strong shock wave into the material. The cluster temperature reaches a maximum of 596 K for 0.1 eV/atom, 1799 K for 1 eV/atom, and 6607 K for 10 eV/atom during the first ps after the touchdown. For energies of 1 and 10 eV/atom the cluster recrystallizes after 20 ps. The consecutive collision of 50 Mo 1043 clusters with a Mo(001) surface at T=300 K was simulated for the three impact energies. The formation of a porous film is calculated for clusters impinging with low kinetic energy, while for the clusters with the highest energy a dense mirrorlike film is obtained, in good agreement with experiment.
Open Access
Molecular dynamics study of implant and damage formation in low-energy boron cluster ion implantation
(Ion Implantation Technology Proceedings, 1998 …, 1999, 1999) Aoki, T.; Matsuo, J.; Insepov, Z.; Yamada, I.
Cluster ion implantation using decaborane (B,J-I,,) has been proposed as a useful technique for shallow junction formation. In order to examine the characteristics and advantages of cluster ion implantation, molecular dynamics simulations of small B cluster and monomer implantation were performed B,, B4 and B,, are irradiated on Si (001) substrates with acceleration energy of 230eV/atom so that B, and 6, are accelerated with 0.Y2keV and 2.3keV, respectively. Those three show the same implant profile and implant efficiency, which agrees with the experimental result of &,,HI, implantation. This result suggests that each B atom in a B cluster acts individually in similar way to a monomer ion. B clusters show the same properties in projection range and implant efficiency as the monomer whereas non-linearity is shown in damage formation. The number of displacements by one B atom once increases to the same maximum value for both a B cluster and a B monomer. However, the damage recovery process is different depending on the cluster sue. Damage induced by B,, recovers more slowly and 4 times as many displacements remain compared to B, 8ps after impact. These displacements by B,, clusters concentrate in the near surface region of the impact point, while the ones by B, reside around the implanted B atom as the end-of-range damage. This characteristic damage formation by B,, cluster is expected to avoid transientenhanced-diffusion of incident B atoms and achieve the formation of high-quality shallow p-type junction.
Open Access
Computer simulation of decaborane implantation and rapid thermal annealing
(IEEE. Ion Implantation Technology Proceedings, 1998 International Conference, 1999-12) Insepov, Z.; Aoki, T.; Matsuo, J.; Yamada, I.
Molecular Dynamics (MD) and Metropolis Monte- Carlo (MMC) models of monomer B and decaborane implantation into Si and following rapid thermal annealing (RTA) processes have been developed. The implanted B dopant and Si-atomic diffusion coefficients were obtained for different substrate temperatures. The simulation of decaborane ion implantation has revealed the formation of an amorphized area in a subsurface region, much larger than that of a single B+ implantation, with the same energy per ion. The calculated B diffusion coefficient has values between 10-'2-10-1c0m 2 s" which agrees well with experimental values obtained for an equilibrium B dopant in Si. Our calculations have shown an unusual temperature dependence with two different activation energies. Low activation energy, less than 0.2 eV, was obtained for a low temperature region, and a higher activation energy, - 3 eV, for a higher-temperature region which is typical for the RTA processing. The higher activation energy is comparable with the equilibrium activation energy, 3.4 eV, for B diffusion in Si. The diffusivity for Si atoms was obtained to be in the interval - l0l2 cm2 s-I. In our present simulation for decaborane cluster implantation into Si, we have not observed the TED phenomenon.
Open Access
Proposal for a hardness measurement technique without indentor by gas-cluster-beam bombardment
(Physical Review B, 2000) Insepov, Z.; Manory, R.; Matsuo, J.; Yamada, I.
Large gas-cluster-ion bombardment has been shown to be a unique tool for generating a variety of bombarding effects over a broad range of acceleration energies. A hardness measurement technique is proposed in this paper based on the use of the effect of crater formation by large gas-cluster beams. The cluster impact leaves a hemispherical crater on a surface, the size of which varies with surface hardness and cluster parameters ~which can be predetermined!. As shown in this paper, the crater depth h ~or diameter d! and Brinell hardness B are correlated through the formula h;(E/B)1/3, where E is the cluster acceleration energy. The material hardness, binding energy, and the crater size have also been correlated with the sputtering yield Y, and hence this correlation can also be experimentally applied for measuring hardness. The proposed method is based entirely on surface effects which depend only on the surface material and not on the substrate and therefore should be particularly suitable for measuring hardness of thin deposited films. This technique also eliminates the need for indentors that are harder than the material measured.
Open Access
Craters on silicon surfaces created by gas cluster ion impacts
(Journal of applied physics, 2002) Allen, L. P.; Insepov, Z.; Fenner, D. B.; Santeufemio, C.; Brooks, W.; Jones, K. S.; Yamada, I.
Atomic force microscopy ~AFM! and high-resolution transmission electron microscope ~HRTEM! cross section imaging of individual gas cluster ion impact craters on Si~100! and Si~111! substrate surfaces is examined. The comparison between 3 and 24 kV cluster impacts from Ar and O2 gas sources is shown. Results for low fluence (1010 ions/cm2) 24 kV Ar individual cluster impacts onto a Si~100! and Si~111! substrate surfaces are compared with hybrid molecular dynamics ~HMD! simulations. A HMD method is used for modeling impacts of Arn (n5135, 225! clusters, with energies of 24–50 eV/atom, on Si~100! and Si~111! surfaces. On a Si~100!, craters are nearly triangular in cross section, with the facets directed along the close-packed ~111! planes. The Si~100! craters exhibit four-fold symmetry as imaged by cross-sectional HRTEM, and AFM top view, in agreement with modeling. In contrast, the shape of craters on a Si~111! shows a complicated six-pointed shape in the modeling, while AFM indicates three-fold symmetry of the impact. The lower energy 3 kV individual cluster impacts reveal the same crater shape in HRTEM cross section for both Ar and O2 gas clusters, but with shallower crater depth than for the higher-energy impacts. The kinetics of the Ar and O2 crater impacts may explain the successful use of higher-energy cluster impacts for etching material of higher initial surface roughness followed by the lower energy impacts as an effective finishing step to achieve smoother surfaces.
Open Access
New mechanism of cluster-field evaporation in rf breakdown
(Physical Review Special Topics-Accelerators and Beams, 2004) Insepov, Z.; Norem, J. H.; Hassanein, A.
Using a simple field evaporation model and molecular dynamics simulations of nanoscale copper tip evolution in a high electric field gradient typical for linacs, we have studied a new mechanism for rf-field evaporation. The mechanism consists of simultaneous (collective) field evaporation of a large group of tip atoms in high-gradient fields. Thus, evaporation of large clusters is energetically more favorable when compared with the conventional, ‘‘one-by-one’’ mechanism. The studied mechanism could also be considered a new mechanism for the triggering of rf-vacuum breakdown. This paper discusses the mechanism and the experimental data available for electric field evaporation of field emission microscopy tips.
Open Access
Radiation-induced synergistic effects of athermal and thermal mechanisms on erosion and surface evolution of advanced electrode and condenser optics materials
(Proceedings of SPIE, 2004-02) Allain, J. P.; Hassanein, A.; Burtseva, T.; Yacout, A.; Insepov, Z.; Taj, S.; Rice, B. J.
In extreme ultraviolet lithography (EUVL) environments transient plasma dynamics dictate conditions for particle/surface interactions. A critical challenge facing EUVL development is optic component lifetime both in gasdischarge produced plasmas (GDPP) and laser-produced plasmas (LPP) devices. Optic components are exposed to impingent species, impurities (H,C,O,N) and debris leading to their degradation and consequently limiting 13.5 nm light reflection intensity. Experiments in the PRIME (Particles and Radiation Interaction with Matter Experiments) facility at the Argonne National Laboratory study the synergy between radiation-induced athermal and thermal mechanisms that influence the behavior of EUVL materials (electrodes and condenser optics) under irradiation conditions including: incident particle energy (50 eV – 5 keV), angle-of-incidence (near-normal to oblique), incident flux (1011-1017 ions/cm2/s), surface coatings (impurity: C,O or capping layers: Ru, W), and surface temperature (100 – 1000 °C). Results of electrode and optical component interaction with singly-charged inert gases (Xe) are presented. Critical issues under study include: radiation enhanced diffusion, radiation induced segregation, preferential sputtering, collisional mixing, surface segregation, surface amorphization, thermal diffusion and thermal spike evolution. Experiments in PRIME will be complemented with atomistic modeling to study how these mechanisms modify surfaces and how these mechanisms can work synergistically to introduce solutions to enhance component lifetime of electrode and condenser optic materials.
Open Access
Breakdown in RF cavities
(Proceedings of 2005 Particle Accelerator Conference, Knoxville, Tennessee, 2005) Norem, J.; Hassanein, A.; Insepov, Z.; Konkashbaev, I.
We present a simple model of breakdown in rf cavities. For most events this involves tensile stress and tensile strength, however other effects can also contribute. We discuss the effects of different materials, fatigue, high pressure gas, primary and secondary emission sites, local field enhancements, dark currents, secondary emission, work functions, magnetic fields, macro and microscopic fracture mechanisms high current densities, surface and subsurface defects, and astronomical power densities. While primarily devoted to normal conductors, this work also has consequences for superconducting rf surfaces.
Open Access
High Surface Fields in Superconducting rf Cavities. In Proceedings of SRF
(Proceedings of the 12th International Workshop on RF Superconductivity, Cornell University, 2005) Norem, J.; Insepov, Z.; Bauer, P.; Seidman, D.N.; Sebastian, J.; Yoon, K.
Field emission in cavities requires electric fields that can be high enough to damage materials. We outline a model of breakdown and field emission from local asperities, and show how electric field effects, and field emission of electrons, field evaporation of ions, ultimately fracture, can limit accelerating fields. Although based on data from copper cavities and preliminary results from atom probe tomography experiments, the model seems to be generally valid for DC to 30 GHz, 10-11 to 105 Torr, different materials, temperatures, conditioning status, secondary emitters, strong magnetic fields, atom probe data, and the variety of surfaces encountered during copper cavity conditioning. We believe studies of normal materials can help to understand mechanisms operating in SCRF, such as fracture, field emission and evaporation effects, control of the surface, and surface metallurgy.
Open Access
Effects of surface damage on rf cavity operation
(Physical Review Special Topics-Accelerators and Beams, 2006) Hassanein, A.; Insepov, Z.; Norem, J.; Moretti, A.; Qian, Z.; Bross, A.; Seidman, D. N.
We describe a model of damage in rf cavities and show how this damage can limit cavity operation. We first present a review of mechanisms that may or may not affect the ultimate fields that can be obtained in rf cavities, assuming that mechanical stress explains the triggers of rf breakdown events. We present a method of quantifying the surface damage caused by breakdown events in terms of the spectrum of field enhancement factors, , for asperities on the surface. We then model an equilibrium that can develop between damage and conditioning effects, and show how this equilibrium can determine cavity performance and show experimental evidence for this mechanism. We define three functions that quantify damage, and explain how the parameters that determine performance can be factored out and measured. We then show how this model can quantitatively explain the dependence of cavity performance on material, frequency, pulse length, gas, power supply, and other factors. The examples given in this paper are derived from a variety of incomplete data sets, so we outline an experimental program that should improve these predictions, provide mechanisms for comparing data from different facilities, and fill in many gaps in the existing data.
Open Access
Requirements for advanced simulation of nuclear reactor and chemicalseparation plants
(Argonne National Laboratory, 2006) Palmiotti, G.; Cahalan, J.; Pfeiffer, P.; Sofu, T.; Taiwo, T.; Wei, T.; Willamson, M.
This report presents requirements for advanced simulation of nuclear reactor and chemical processing plants that are of interest to the Global Nuclear Energy Partnership (GNEP) initiative. Justification for advanced simulation and some examples of grand challenges that will benefit from it are provided. An integrated software tool that has its main components, whenever possible based on first principles, is proposed as possible future approach for dealing with the complex problems linked to the simulation of nuclear reactor and chemical processing plants. The main benefits that are associated with a better integrated simulation have been identified as: a reduction of design margins, a decrease of the number of experiments in support of the design process, a shortening of the developmental design cycle, and a better understanding of the physical phenomena and the related underlying fundamental processes. For each component of the proposed integrated software tool, background information, functional requirements, current tools and approach, and proposed future approaches have been provided. Whenever possible, current uncertainties have been quoted and existing limitations have been presented. Desired target accuracies with associated benefits to the different aspects of the nuclear reactor and chemical processing plants were also given. In many cases the possible gains associated with a better simulation have been identified, quantified, and translated into economical benefits.
Open Access
The Interactions of Surface Damage on RF Cavity Operation
(Fermilab, 2006-06) Norem, J.; Bross, A.; Hassanein, A.; Qian, Z.; Yoon, K. E.; Moretti, A.; Li, D.
Studies of low frequency RF systems for muon cooling has led to a variety of new techniques for looking at dark currents, a new model of breakdown, and, ultimately, a model of RF cavity operation based on surface damage. We find that cavity behavior is strongly influenced by the spectrum of enhancement factors on field emission sites.Three different spectra are involved: one defining the initial state of the cavity, the second determined by the breakdown events, and the third defining the equilibrium produced as a cavity operates at its maximum field. We have been able to measure these functions and use them to derive a wide variety of cavity parameters: conditioning behavior, material, pulse length, temperature, vacuum, magnetic field, pressure, gas dependence. In addition we can calculate the dependence of breakdown rate on surface field and pulse length. This work correlates with data from Atom Probe Tomography. We will describe this model and new experimental data.
Open Access
Computer simulation of bubble formation
(Joint International Topical Meeting on Mathematics & Computation and Supercomputing in Nuclear Applications, 2007-04) Insepov, Z.; Bazhirov, T.; Norman, G.; Stegailov, V.
Properties of liquid metals (Li, Pb, Na) containing nanoscale cavities were studied by atomistic Molecular Dynamics (MD). Two atomistic models of cavity simulation were developed that cover a wide area in the phase diagram with negative pressure. In the first model, the thermodynamics of cavity formation, stability and the dynamics of cavity evolution in bulk liquid metals have been studied. Radial densities, pressures, surface tensions, and work functions of nano-scale cavities of various radii were calculated for liquid Li, Na, and Pb at various temperatures and densities, and at small negative pressures near the liquid-gas spinodal, and the work functions for cavity formation in liquid Li were calculated and compared with the available experimental data. The cavitation rate can further be obtained by using the classical nucleation theory (CNT). The second model is based on the stability study and on the kinetics of cavitation of the stretched liquid metals. A MD method was used to simulate cavitation in a metastable Pb and Li melts and determine the stability limits. States at temperatures below critical (T < 0.5Tc) and large negative pressures were considered. The kinetic boundary of liquid phase stability was shown to be different from the spinodal. The kinetics and dynamics of cavitation were studied. The pressure dependences of cavitation frequencies were obtained for several temperatures. The results of MD calculations were compared with estimates based on classical nucleation theory.
Open Access
Surface erosion and modification by highly charged ions
(Physical Review A, 2008) Insepov, Z.; Terasawa, M.; Takayama, K.
Analyses were conducted of various models and mechanisms of highly charged ion HCI and swift-heavy ion energy transfer into a solid target, such as hollow atom formation, charge screening, neutralization, shock wave generation, crater formation, and sputtering. A plasma model of space charge neutralization based on impact ionization of semiconductors at high electric fields was developed and applied to analyze HCI impacts on Si and W. Surface erosion of semiconductor and metal surfaces caused by HCI bombardments were studied by using a molecular dynamics simulation method, and the results were compared with experimental sputtering data.
Open Access
A model of rf breakdown arcs
(Fermilab, 2008) Insepov, Z.; Bross, A.; Qian, Z.; Norem, J.; Huang, D.; Veitzer, S.; Torun, Y.
This paper presents a rst iteration of a model that attempts to describe all aspects of breakdown in rf cavities and provides some estimates of the parameters and parameter ranges involved, as an aid to producing more precise models and more useful experiments. The model describes how breakdown events can be triggered, how they grow, it identi es the power source for their rapid growth, mechanisms that limit their growth, how they are extinguished and how they can be mitigated. We also discuss applications to superconducting rf and high pressure gas structures. The model relies heavily on previous experiments with 805 and 201 MHz warm copper cavities, and pre-liminary plasma modeling using the code OOPIC Pro. We compare estimates from the model with experimental data where this is possible. Because of the geometrical dependence of all parameters, the wide range of experiments being performed, the wide range of experimental parameters in a given breakdown event and the lack of extensive systematic parameter searches at this stage in our studies, it is diffcult to present precise results. We are constrained to showing what mechanisms are involved, the strength of these mechanisms and how they interact to produce the experimental data. We are primarily interested in the development and dynamics of the arc, magnetic and gas effects and insights on how to avoid arcing in all environments.
Open Access
A design for large-area fast photo-detectors with transmission-line readout and waveform sampling
(In Real Time Conference, 2009. RT'09. 16th IEEE-NPSS (pp. 49-61). IEEE., 2009) Adams, B.; Anderson, J. T.; Attenkofer, K.; Bogdan, M.; Byrum, K.; Drake, G.; Insepov, Z.
We present a preliminary design and the results of simulation for a photo-detector module to be used in applications requiring the coverage of areas of many square meters with time resolutions less than 10 picoseconds and position resolutions of less than a millimeter for charged particles. The source of light is Cherenkov light in a radiator/window; the amplification is provided by panels of micro-pores functionalized to act as microchannel plates (MCPs). The good time and position resolution stems from the use of an array of parallel 50 Ω transmission lines (strips) as the collecting anodes. The anode strips feed multi-GS/sec sampling chips which digitize the pulse waveform at each end of the strip, allowing a measurement of the time from the average of the two ends, and a 2-dimensional position measurement from the difference of times on a strip, and, in the orthogonal direction, the strip number, or a centroid of the charges deposited on adjacent strips. The module design is constructed so that large areas can be `tiled' by an array of modules.
Open Access
Advanced Surface Polishing For Accelerator Technology Using Ion Beams
(American Institute of Physics, 2009-03) Insepov, Z.; Norem, J.; Hassanein, A.; Wu, A. T.
Surface erosion problems are common in the development of TeV accelerators, fusion and fission reactors, semiconductor, optical and magnetic storage devices, and Extreme Ultra-Violet (EUV) lithography devices. We have reviewed various erosion mechanisms of ion interactions with the surfaces studied by experiment and computer simulation. Nanoscale surface roughness in rf-linacs and contamination cause field emission of electrons, field evaporation of ions and fragments, plasma formation, and lead to high-gradient rf vacuum breakdown of electrodes which is a limiting factor in the development of high-gradient rf technology for future TeV accelerators. A few mechanisms of nanoscale surface fracture under a high-gradient electric field were developed and will be discussed. A Gas Cluster Ion Beam (GCIB) technology was successfully applied to surface treatment of Cu, Stainless steel, Ti and Nb samples and to Nb rf-cavities by using accelerated cluster ion beams of Ar, O2, N2, and NF3, and combinations of them, with accelerating voltages up to 35 kV. DC field emission (dark current) measurements and electron microscopy were used to investigate metal surfaces treated by GCIB. The experimental results showed that GCIB technique can significantly reduce the number of field emitters and also change the structure of the Nb oxide layer on the surface. The RF tests on the GCIB treated Nb rf-cavities showed improvement of the quality factor Q at 4.5 K. The superconducting gap was also enhanced by using the oxygen GCIB irradiation exposure. GCIB may become a standard technique to modify and control the oxygen content on the surface and a promising surface treatment technique for Nb SRF cavities in particle accelerators. Computer simulation of bombardment of Nb surfaces with Ar and O2 clusters by molecular dynamics and phenomenological surface dynamics equations confirms experimental results.
Open Access
A New Multiscale Approach to Nuclear Fuel Simulations: Atomistic Validation of Kinetic Method
(Transactions of the American Nuclear Society, 2010) Insepov, Z.; Rest, J.; Hofman, G. L.; Yacout, A.; Norman, G. E.; Starikov, S. A.; Stegailov, V. V.
A key issue for fuel behavior codes is their sensitivity to values of various materials properties, many of which have large uncertainties or have not been measured. Kinetic mesoscale models, such as those developed at Argonne National Laboratory within the past decade, are directly comparable to data obtained from in-reactor experiments. In the present paper, a new multiscale concept is proposed that consists of using atomistic simulation methods to verify the kinetic approach. The new concept includes kinetic rate-equations for radiation damage, energetics and kinetics of defects, and gas/defect-driven swelling of fuels as a function of temperature and burnup. The quantum and classical atomistic simulation methods are applied to increase our understanding of radiation damage and defect formation and growth processes and to calculate the probabilities of elemental processes and reactions that are applicable to irradiated nuclear materials.
Open Access
MECHANISTIC INSIGHT INTO THE ROLE OF POLY(ADP-RIBOSYL)ATION IN DNA TOPOLOGY MODULATION AND RESPONSE TO DNA DAMAGE
(Mutagenesis, 2010) Matkarimov, Bakhyt T.; Zharkov, Dmitry O.; Saparbaev, Murat K.
Genotoxic stress generates single- and double-strand DNA breaks either through direct damage by reactive oxygen species or as intermediates of DNA repair. Failure to detect and repair DNA strand breaks leads to deleterious consequences such as chromosomal aberrations, genomic instability and cell death. DNA strand breaks disrupt the superhelical state of cellular DNA, which further disturbs the chromatin architecture and gene activity regulation. Proteins from the poly(ADP ribose) polymerase (PARP) family, such as PARP1 and PARP2, use NAD+ as a substrate to catalyse the synthesis of polymeric chains consisting of ADP-ribose units covalently attached to an acceptor molecule. PARP1 and PARP2 are regarded as DNA damage sensors that, upon activation by strand breaks, poly(ADP-ribosyl)ate themselves and nuclear acceptor proteins. Noteworthy, the regularly branched structure of poly(ADP-ribose) polymer suggests that the mechanism of its synthesis may involve circular movement of PARP1 around the DNA helix, with a branching point in PAR corresponding to one complete 360° turn. We propose that PARP1 stays bound to a DNA strand break end, but rotates around the helix displaced by the growing poly(ADP-ribose) chain, and that this rotation could introduce positive supercoils into damaged chromosomal DNA. This topology modulation would enable nucleosome displacement and chromatin decondensation around the lesion site, facilitating the access of DNA repair proteins or transcription factors. PARP1-mediated DNA supercoiling can be transmitted over long distances, resulting in changes in the high-order chromatin structures. The available structures of PARP1 are consistent with the strand break induced PAR synthesis as a driving force for PARP1 rotation around the DNA axis.