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Jari Koskinen

Bio: Jari Koskinen is an academic researcher from Aalto University. The author has contributed to research in topics: Amorphous carbon & Thin film. The author has an hindex of 32, co-authored 161 publications receiving 3587 citations. Previous affiliations of Jari Koskinen include Cornell University & University of Helsinki.


Papers
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Journal ArticleDOI
04 Feb 2007-Wear
TL;DR: In this article, the effect of microtexturing of sliding surfaces by laser ablation and polishing was investigated, based on two independent experimental approaches with oil-lubricated smooth and laser-textured steel surfaces in oscillating sliding contact with a steel ball.

230 citations

Journal ArticleDOI
01 May 2001-Wear
TL;DR: In this article, the effect of graphitization on the friction performance of amorphous hydrogenated carbon films (a-C:H) and hydrogen-free tetrahedral ammorphous carbon (ta-C) was investigated.

194 citations

Journal ArticleDOI
TL;DR: In this paper, a comprehensive characterization of the stress, elastic modulus, hardness and adhesion of ALD aluminum oxide (Al2O3) films grown at 110-300°C from trimethylaluminum and water is presented.

144 citations

Journal ArticleDOI
TL;DR: In this paper, the authors analysed the stress and fracture conditions of a coated surface, that are the origin to wear, by three-dimensional finite element method (FEM) modelling on micro-level, by stress and strain computer simulations and by experimental studies with a scratch tester.
Abstract: The stress and fracture conditions of a coated surface, that are the origin to wear, were analysed by three-dimensional finite element method (FEM) modelling on microlevel, by stress and strain computer simulations and by experimental studies with a scratch tester The studied tribological contact was a 02 mm radius diamond ball sliding with increasing load on a thin, 2 Am thick titanium nitride (TiN) coating on a flat high speed steel substrate The ball was modelled as rigid, the coating linearly elastic and the steel substrate elastic–plastic taking into account strain hardening effects The stresses and strains generated in the surface during sliding are the result of four different mechanisms: the pulling and pushing by the friction force; the geometrical indent, groove, and torus shaped deformations of the flat surface; the bulk plasticity concentration and curvature minimum effects; and the residual stresses in the coating In a sliding contact the first crack is initiated at the top of the coating from bending and pulling actions and it grows down through the coating In the modelled scratch tester system a complex stress field is formed at the surface including remaining residual stresses in the coating behind the sliding contact The stress fields are very different in a scratched uncoated steel sample Some residual tensile stresses are formed in the groove behind the tip but they are very much lower than for the TiN coated case A displacement controlled FEM model was found to better represent the real situation and correspond to experimental results than a force controlled model D 2005 Elsevier BV All rights reserved

134 citations

Journal ArticleDOI
TL;DR: The erosive effect of some commonly used acidic drinks and milk products on a bovine tooth enamel model system is useful for comparative purposes but cannot be directly extended to the oral cavity under normal use conditions.
Abstract: – The objective was to compare the erosive effect of some commonly used acidic drinks and milk products on a bovine tooth enamel model system. Conditions were selected to be sufficiently severe to cause erosion. Loss of material after erosion experiments was measured by recording the depth of the surface profile after repeated and prolonged exposure. Changes in the enamel surface were observed by scanning electron microscopy. The reparative mechanisms were studied by immersing test teeth in saliva, with or without (2 ppm) fluoride, after severe demineralization in the test products. According to the t-test for paired means, cola beverages and orange beverages differed from beer, coffee with or without sugar, strawberry yoghurt, buttermilk, and carbonated mineral water at the level P0.01. Each of the last-mentioned test products differed from sports drinks, diet cola beverages and orange juice less significantly. In addition, bathing of teeth in saliva between exposures to the test products did not influence the erosive depth. The results, based on in vitro conditions that ensured erosion, are useful for comparative purposes but cannot be directly extended to the oral cavity under normal use conditions.

131 citations


Cited by
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01 May 1993
TL;DR: 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.
Abstract: 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.

29,323 citations

Journal ArticleDOI
TL;DR: In this paper, the authors describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of diamond-like carbon.
Abstract: 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).

5,400 citations

Journal ArticleDOI
TL;DR: Diamond-like carbon (DLC) films have attracted an overwhelming interest from both industry and the research community as mentioned in this paper, and they offer a wide range of exceptional physical, mechanical, biomedical and tribological properties that make them commercially essential for numerous industrial applications.
Abstract: 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)

1,046 citations

Journal ArticleDOI
12 Sep 2014-Science
TL;DR: This work demonstrates 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.
Abstract: 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.

1,044 citations

Journal ArticleDOI
TL;DR: The goal of this paper is to demonstrate that AFM is capable of producing atomic-scale knowledge, and to focus upon some of the contributions of the AFM to nanotribology.
Abstract: 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

1,013 citations