Presentation on theme: "COSIRES2004 MD Simulation of Surface Smoothing due to Cluster Impact: Estimation of Radiation Damage T.Muramoto, K.Itabasi and Y.Yamamura Okayama University."— Presentation transcript:
1COSIRES2004MD Simulation of Surface Smoothing due to Cluster Impact: Estimation of Radiation DamageT.Muramoto, K.Itabasi and Y.YamamuraOkayama University of Science, Department of InformaticsRidai-cho 1-1, Okayama , JapanThe radiation damage of irradiated surfaces by cluster ion with a few eV/atom is studied through MD simulations, where (Ar)3055 clusters with 3-10eV/atom are bombarded on a rough Cu surface.
2Collision cascade100fs: Channeling is found.150fs: Dechanneling is caused.250fs: Most of cascade is formed.400fs: Focusing is appeared.Finally, Frenkel defect is induced by monatomic ion beam.Using DYACOCT code dynamical simulation of atomic collision in crystal target based on binary-collision approximation
3Feature of Cluster ion beam Chemical-mechanical polishingStandard smoothing technology. Wet process using chemical abrasive and grinding pad. Unsuitable for soft material. Surface cleaning is essential to the contamination.Ionized cluster beamLow charge and velocity. High energy and particle density. Beam intensity consistent hardly with control of cluster size.Low velocity and charge to mass ratio leads to low damage.High particle density formation.Explosion to lateral direction.High deposited energy density results in high-yield sputtering.
4Measurement of fractal surface Monolayer mole numbers on porous silica gel as a function of molecule cross-section.Surface may be rough and even fractal down to the molecular size range.D=3.02±0.06[P.Pfeifer, D.Avnir and D.Farin, J. Stat. Phys. 36 (1984) 699.]
5Fractal Similarity dimension D=logA/logB: A parts, scaled by ratio 1/B Shape and phenomena with non-characteristic scaleFractal is characterized by dimension with non-integer value.Similarity dimension D=logA/logB: A parts, scaled by ratio 1/BLine2 parts, scaled by ratio 1/2The von Koch snowflake curve4 parts, scaled by ratio 1/34 parts, scaled by ratio 1/2Plane
6Contents 1. MD simulation model 2. Surface smoothing 1.1. Projectile and target information, interatomic potentials1.2. Control of target temperature1.3. Initial rough surface and fractal2. Surface smoothing3. Radiation damage3.1. Criterion of damage type3.2. Quantification of damage3.3. Thickness of damage layer
8Control of target temperature Cool downby LMD layerTotal kinetic energyof target atomsCluster energyNumerical cool down300K1st2ndTime of simulated system
9Shock wave in view of temperature This is a color map of temperature in cross-section. It found that the shock wave reflect at bottom. Average sputter yields are 58 and 54, respectively. This difference is not a significant error.
146.5eV/atom (Ar)3055Sputter yield per impact = 5.9, RMS Roughness = nmExperiment: 50 ion/nm2, 20keV Ar3000 bombardment on Cu[H. Kitani et al., Nucl. Instrm. Meth. B121 (1997) 489.]
15Development of average roughness Final roughness is determined bythe magnitude of surface modification by individual cluster impact.Fractal surface satisfies the scaling relation of self-affine:Z(ax,ay)=a3-DZ(x,y).[J.Feder, FRACTALS, Plenum, New York, 1985.]
16Radial distribution: 10eV/atom The irradiated targets are cooled down to 3K in 50ps using LMD method for the whole target atoms.
21Crystal grainMelting and crystallization of impact region produced grain.
22Number of first neighbors = 11 There are cage and linear groups near the impact region.
23VacancyThis is a quenched-in vacancy when target cooled down to 300K.
24DivacancyThis is a quenched-in vacancy when target cooled down to 300K.
25Vacancy clusterThis is a quenched-in vacancy when target cooled down to 300K.
26DislocationNumber of first neighbors is 13 (red) and 11 (blue). Green symbol is stacking fault atoms.ABCABCACABCAThis is an edge dislocation. The tensile and compressive stress acts on the red and blue atom, respectively.
30Thickness of damage layer Thickness are about 8nm (10eV/atom) and 4nm (3eV/atom).
31SummaryThe average roughness due to 6.5eV/atom cluster bombardments ranges about nm, which is less than the result of experiment* from the smallness of target in this simulation.There is no Frenkel pair, because the cluster impact with a few eV/atom cannot produce the energetic PKA.In the impact region, the high temperature results in a few vacancy and grain, and the high pressure generates some dislocation and stacking fault.The pressing effect is important than the thermal effect to induce the damage in the big cluster impact with a few eV/atom.The big cluster ion can affects only near the surface, which the thickness of damage layer is about 4-8nm for 3-10eV/atom.* H. Kitani, N. Toyoda, J. Matsuo and I. Yamada , Nucl. Instrm. Meth. B121 (1997) 489.
32Acknowledgement This work was supported by a Grant of The Academic Frontier Project promoted by The Ministry of Education,Culture, Sports, Science and Technology of Japan.