Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

X-ray photoelectron spectroscopy: Towards reliable binding energy referencing

https://www.diva-portal.org/smash/get/diva2:17175/FULLTEXT02

Ionized physical vapor deposition (IPVD): A review of technology and applications

http://liu.diva-portal.org/smash/get/diva2:303552/FULLTEXT01

The Mn+1AXn phases: Materials science and thin-film processing

High power pulsed magnetron sputtering (HPPMS) is an emerging technology that has gained substantial interest among academics and industrials alike. HPPMS, also known as HIPIMS (high power impulse ...

High power pulsed magnetron sputtering: A review on scientific and engineering state of the art

The energy distributions of O− ions of magnetron sputtered Nb, Ta, Zr, and Hf in an Ar∕O2 atmosphere were measured as a function of the oxygen partial pressure. Three ion populations were detected in the plasma: high, medium, and low energy ions, with energies corresponding to the target potential, half of the target potential, and <150eV, respectively. The ion energy distribution functions were compared to distributions obtained based on Sigmund’s linear collision cascade sputtering theory. If the surface binding energy is assumed to be equal to the heat of formation, good agreement between the experiment and theory was achieved. From correlating the measured ion energy distributions with previously published phase stability data [Ngaruiya et al., Appl. Phys. Lett. 85, 748 (2004)], it can be deduced that large fluxes of medium and high energy O− ions comparable to the fluxes of the low energy O− ions enable formation of crystalline transition metal oxide thin films during low temperature growth. The pres...

Influence of the negative oxygen ions on the structure evolution of transition metal oxide thin films

The evolution of the coating stoichiometry with pressure, target-substrate distance, and angle was analyzed for dc sputtering of TixB (x=0.5, 1, 1.6) compound targets by elastic recoil detection analysis. For an investigation of the underlying fundamental processes primarily Ar was used as sputter gas. Additionally, the effect of a reactive gas (N2) as well as bias voltage (floating up to −200 V) was briefly cross-checked. For deposition along the target normal (90°) a pronounced Ti-deficiency of up to 20% is detected. Increasing the pressure or distance from 0.5 to 2 Pa and from 5 to 20 cm, respectively, leads to an almost equivalent linear increase in Ti/B ratio surpassing even the target composition. Off-axis depositions at lower angles (30° and 60°) on the other hand result in a higher Ti/B ratio. This is consistent with results obtained from Monte Carlo simulations combining the respective emission characteristics from the sputter process as well as the gas-phase transport. Hence, the pressure, dista...

Experiment and simulation of the compositional evolution of Ti–B thin films deposited by sputtering of a compound target

The physical reason for the apparently low deposition rate during high-power pulsed magnetron sputtering

Amorphous carbon films are deposited employing high power impulse magnetron sputtering (HiPIMS) at pulsing frequencies of 250 Hz and 1 kHz. Films are also deposited by direct current magnetron sputtering (dcMS), for reference. In both HiPIMS and dcMS cases, unipolar pulsed negative bias voltages up to 150 V are applied to the substrate to tune the energy of the positively charged ions that bombard the growing film. Plasma analysis reveals that HiPIMS leads to generation of a larger number of ions with larger average energies, as compared to dcMS. At the same time, the plasma composition is not affected, with Ar + ions being the dominant ionized species at all deposition conditions. Analysis of the film properties shows that HiPIMS allows for growth of amorphous carbon films with sp 3 bond fraction up to 45% and density up to 2.2 g cm − 3 . The corresponding values achieved by dcMS are 30% and 2.05 g cm − 3 , respectively. The larger fraction of sp 3 bonds and mass density found in films grown by HiPIMS are explained in light of the more intense ion irradiation provided by the HiPIMS discharge as compared to the dcMS one.

/pdf/exploring-the-potential-of-high-power-impulse-magnetron-56wiy6s092.pdf

Exploring the potential of high power impulse magnetron sputtering for growth of diamond-like carbon films

Low, medium, and high energy O− ion populations were experimentally detected during magnetron sputtering of Al in an Ar∕O2 atmosphere. Based on calculations, the authors propose that nonsputtered O− ions originating from the target surface are accelerated in the cathode fall, while sputtered O− ions may be excluded as a significant contribution to the high energy ion population. Furthermore, the formation of medium energy O− ions is consistent with the notion of sputtered, in the cathode fall accelerated, and subsequently dissociated AlO− and AlO2− clusters. These findings may be of importance for understanding plasma energetics and growth involving electronegative species.

Stanislav Mráz

Papers

Influence of the negative oxygen ions on the structure evolution of transition metal oxide thin films

Experiment and simulation of the compositional evolution of Ti–B thin films deposited by sputtering of a compound target

The physical reason for the apparently low deposition rate during high-power pulsed magnetron sputtering

Exploring the potential of high power impulse magnetron sputtering for growth of diamond-like carbon films

Energy distribution of O− ions during reactive magnetron sputtering