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.

Hard‐carbon layers were deposited on WC‐Co hard‐metal substrates using mass‐separated 12C+‐ion beams with ion energies varying between 10 eV and 2 keV. The abrasive wear resistance, hardness, density, and dc resistance of these films were measured as a function of ion energy. Coatings deposited at ion energies between 100 eV and 2 keV possessed the highest hardness, best wear resistance, and good adhesion to the substrate, whereas coatings prepared at ion energies Ei ≤50 eV suffered from poor adhesion. The resistance of the hard‐carbon coating against the abrasive wear was found to be about 300 times better than that of a typical ceramic Al2O3. In addition, Vickers hardness 120±20 GPa, density 3.3±0.3 g/cm3, and dc resistance 2×109 Ω cm were obtained. The hardness was found to remain unchanged after the thermal annealing up to 600 °C.

Abrasive wear resistance of ion‐deposited hard‐carbon films as a function of deposition energy

In this study we demonstrate a scalable and CMOS compatible synthesis of robust diamond-like carbon (DLC)–multi-walled carbon nanotube (MWCNT) hybrid electrodes. MWCNTs were grown directly on top of DLC thin film electrodes by utilizing Al/Co/Fe tri-layer catalyst structure at 550 °C. The structure of the hybrid material was characterized in detail by utilizing scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman investigations and X-ray photoelectron spectroscopy (XPS). After a very simple activation step with nitric acid the material was shown to exhibit a wide stable water window, almost reversible electron transfer kinetics and high sensitivity as well as selectivity towards dopamine (DA) in the presence of ascorbic acid (AA). Thus, it can be argued that the electrochemical properties of DLC and MWCNT were combined in a unique way in this new hybrid nanomaterial. The possible reasons behind the observed behavior are discussed in considerable detail. Despite the fact that present results are valid only for this particular hybrid material synthesized under conditions described in this paper, we anticipate that by utilizing the concept of DLC–MWCNT hybrids, several other novel carbon based electrode materials may be introduced for a wide variety of electrochemical and other applications.

Carbon nanotube (CNT) forest grown on diamond-like carbon (DLC) thin films significantly improves electrochemical sensitivity and selectivity towards dopamine

Diamond-like carbon (DLC) coatings have shown excellent tribological properties in laboratory tests The coatings have also been introduced to several practical applications However, the functional reliability of the coatings is often weakened by adhesion and load-carrying capacity related problems In this study the load-carrying capacity of the coating/substrate system has been evaluated The DLC coatings were deposited on stainless steel, alumina and cemented carbide with two different deposition techniques: the tetrahedral amorphous carbon (ta-C) coatings were deposited by a pulsed vacuum arc discharge deposition method and the hydrogenated carbon (a-C:H) films by radio frequency (rf) plasma deposition method The load-carrying capacity of the coated systems was evaluated using a scratch test, Rockwell C-indentation test and ball-on-disc test The effect of substrate material, substrate hardness, coating type and coating thickness was studied An increase in substrate hardness increased the load-carrying capacity for the coated systems, as expected The two coating types exhibited different performance under load due to their different physical and mechanical properties For the load-carrying capacity evaluations the ball-on-disc configuration was found to be most suitable

Load-carrying capacity evaluation of coating/substrate systems for hydrogen-free and hydrogenated diamond-like carbon films

http://rua.ua.es/dspace/bitstream/10045/40704/2/2014_Laurila_etal_D%26RM.pdf

New electrochemically improved tetrahedral amorphous carbon films for biological applications

Unmodified and multi-walled carbon nanotube modified tetrahedral amorphous carbon (ta-C) films as in vivo sensor materials for sensitive and selective detection of dopamine

Jari Koskinen

Papers

Abrasive wear resistance of ion‐deposited hard‐carbon films as a function of deposition energy

Carbon nanotube (CNT) forest grown on diamond-like carbon (DLC) thin films significantly improves electrochemical sensitivity and selectivity towards dopamine

Load-carrying capacity evaluation of coating/substrate systems for hydrogen-free and hydrogenated diamond-like carbon films

New electrochemically improved tetrahedral amorphous carbon films for biological applications

Unmodified and multi-walled carbon nanotube modified tetrahedral amorphous carbon (ta-C) films as in vivo sensor materials for sensitive and selective detection of dopamine