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

Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

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Diamond-like amorphous carbon

During the past two decades, diamond-like carbon (DLC) films have attracted an overwhelming interest from both industry and the research community. These films offer a wide range of exceptional physical, mechanical, biomedical and tribological properties that make them scientifically very fascinating and commercially essential for numerous industrial applications. Mechanically, certain DLC films are extremely hard (as hard as 90 GPa) and resilient, while tribologically they provide some of the lowest known friction and wear coefficients. Their optical and electrical properties are also extraordinary and can be tailored to meet the specific requirements of a given application. Because of their excellent chemical inertness, these films are resistant to corrosive and/or oxidative attacks in acidic and saline media. The combination of such a wide range of outstanding properties in one material is rather uncommon, so DLC can be very useful in meeting the multifunctional application needs of advanced mechanical systems. In fact, these films are now used in numerous industrial applications, including razor blades, magnetic hard discs, critical engine parts, mechanical face seals, scratch-resistant glasses, invasive and implantable medical devices and microelectromechanical systems. DLC films are primarily made of carbon atoms that are extracted or derived from carbon-containing sources, such as solid carbon targets and liquid and gaseous forms of hydrocarbons and fullerenes. Depending on the type of carbon source being used during the film deposition, the type of bonds (i.e. sp 1 ,s p 2 ,s p 3 ) that hold carbon atoms together in DLC may vary a great deal and can affect their mechanical, electrical, optical and tribological properties. Recent systematic studies of DLC films have confirmed that the presence or absence of certain elemental species, such as hydrogen, nitrogen, sulfur, silicon, tungsten, titanium and fluorine, in their microstructure can also play significant roles in their properties. The main goal of this review paper is to highlight the most recent developments in the synthesis, characterization and application of DLC films. We will also discuss the progress made in understanding the fundamental mechanisms that control their very unique friction and wear behaviours. Novel design concepts and the principles of superlubricity in DLC films are also presented. (Some figures in this article are in colour only in the electronic version)

https://iopscience.iop.org/article/10.1088/0022-3727/39/18/R01/pdf

Tribology of diamond-like carbon films: recent progress and future prospects

Ceramics have some of the highest strength- and stiffness-to-weight ratios of any material but are suboptimal for use as structural materials because of their brittleness and sensitivity to flaws. We demonstrate the creation of structural metamaterials composed of nanoscale ceramics that are simultaneously ultralight, strong, and energy-absorbing and can recover their original shape after compressions in excess of 50% strain. Hollow-tube alumina nanolattices were fabricated using two-photon lithography, atomic layer deposition, and oxygen plasma etching. Structures were made with wall thicknesses of 5 to 60 nanometers and densities of 6.3 to 258 kilograms per cubic meter. Compression experiments revealed that optimizing the wall thickness-to-radius ratio of the tubes can suppress brittle fracture in the constituent solid in favor of elastic shell buckling, resulting in ductile-like deformation and recoverability.

Strong, lightweight, and recoverable three-dimensional ceramic nanolattices

A few years after the invention of the scanning tunneling microscope (STM), the atomic force microscope (AFM) was developed Instead of measuring tunneling current, a new physical quantity could be investigated with atomic-scale resolution: the force between a small tip and a chosen sample surface This paper reviews progress and recent results obtained with AFM and other closely related techniques in the field of nanotribology, and attempts to point out many of the unresolved questions that remain The goal of this paper is to demonstrate that AFM is capable of producing atomic-scale knowledge As such, the authors will focus upon some of the contributions of the AFM to nanotribology They will almost exclusively discuss results that shed light on the actual atomic and molecular processes taking place, as opposed to the more applied investigations of microscale properties which are also carried out with AFM They will accompany this discussion by mentioning related theoretical efforts and simulations, although their main emphasis will be upon experimental results and the techniques used to obtain them, as well as suggested future directions In many ways, AFM techniques for quantitative, fundamental nanotribology are only in a nascent stage; certain key issues such as force calibration,more » tip characterization, and the effects of the experimental environment, are not fully resolved or standardized The authors thus begin with a critical discussion of the relevant technical aspects with using AFM for nanotribology 289 refs« less

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Scratching the Surface: Fundamental Investigations of Tribology with Atomic Force Microscopy.

Functionalized Nanocellulose/Multiwalled Carbon Nanotube Composites for Electrochemical Applications

The role of extra carbon source during the pre-annealing stage in the growth of carbon nanofibers

Single walled carbon nanotube network (SWCNTN) was coated by tetrahedral amorphous carbon (ta-C) using a pulsed Filtered Cathodic Vacuum Arc system to form a SWCNTN—ta-C composite film. The effects of SWCNTN areal coverage density and ta-C coating thickness on the composite film properties were investigated. X-Ray photoelectron spectroscopy measurements prove the presence of high quality sp3 bonded ta-C coating on the SWCNTN. Raman spectroscopy suggests that the single wall carbon nanotubes (SWCNTs) forming the network survived encapsulation in the ta-C coating. Nano-mechanical testing suggests that the ta-C coated SWCNTN has superior wear performance compared to uncoated SWCNTN.

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Single walled carbon nanotube network—Tetrahedral amorphous carbon composite film

Nanolayered gradient structures as an intermediate layer for diamond coatings

PUHTEET 2 and 3 projects focused on study of thin film coatings (sol-gel and ALD-based) which are aimed to provide additional value for different metal materials and products. The aim was to gain the long term corrosion and wear resistance, anti-scratch and easy-to-clean properties as well as take into account the decorative aspects. In addition, the suitability of the sol-gel coatings for roll-to-roll (R2R) coating of metallic coils was investigated. Furthermore, novel surface pre-treatments (PET-electric disharhage, atmospheric plasma, and dry ice cleaning) to be used for cleaning of metallic substrates prior deposition of sol-gel coating were studied. Coating development concentrated on the influence of inorganic (e.g. SiO2, Al2O3, ZrO2) and organic (e.g. vinyl, acryl, metacryl and epoxy) components to desired properties of the coatings. Also, the effectivity of the corrosion inhibitors and influence on different dyeing agents were investigated. The effect of different curing methods and processes for sol-gel based coatings were investigated as well as industrial scale and industrial environment coating procedures. A novel pre-treatment method (electropolishing with electric discharge method, PET) using environmentally ammonium sulphate based electrolytes was investigated and it was found to be feasible also in continuous process for metal coils. Dry ice (solid CO2) cleaning was also studied as a pre-treatment method for a reel-to-reel coating of metal coils. It was found that the dry ice treatment produces sufficient surface quality for further surface coating with sol-gel coatings and good adhesion of the coating, especially when used with copper based materials which are sensitive for oxidation after a traditional surface pre-treatment. A novel forming method (Incremental Sheet Forming) was used for moulding of sol-gel coated metal sheets to investigate the behaviour of the coatings and influence of forming parameters. Sol-gel coated metal sheets could be formed with this method and the coatings resisted forming in some level though the forming parameters and properties of the coatings had very strong effect on degradation of the coating. Environmental aspects of the sol-gel coatings were investigated. It was verified that all the coatings used in the project fulfilled the demands concerning volatile organic compound (VOC) emissions set by the directive 2004/42/EC. The long-term corrosion resistance and dirt repellancy of the coated materials were investigated with the field corrosion tests on an isle located in the Gulf of Finland. The duration of the tests was around 550 days. Only the thickest coatings (ca. 3050 μm) were still protecting the base material after this environmental exposure. Thinner sol-gel coatings with a thickness of sub-micrometer to couple of micrometers or ALD/TiO2-coatings with a thickness of couple of tens or hundreds of nanometers could not fully protect the base material, especially if the base

Jari Koskinen

Papers

Functionalized Nanocellulose/Multiwalled Carbon Nanotube Composites for Electrochemical Applications

The role of extra carbon source during the pre-annealing stage in the growth of carbon nanofibers

Single walled carbon nanotube network—Tetrahedral amorphous carbon composite film

Nanolayered gradient structures as an intermediate layer for diamond coatings

Hybridipinnoitteilla lisäarvoa metallituotteille