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Tomi Laurila - One of the best experts on this subject based on the ideXlab platform.
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multiwalled Carbon nanotubes nanofibrillar cellulose nafion composite modified Tetrahedral Amorphous Carbon electrodes for selective dopamine detection
Journal of Physical Chemistry C, 2019Co-Authors: Vasuki Durairaj, Niklas Wester, Tomi Laurila, Jarkko Etula, Janika Lehtonen, Orlando J Rojas, Nikolaos Pahimanolis, Jari KoskinenAbstract:We introduce a composite membrane comprised of multiwalled Carbon nanotubes (MWCNTs) dispersed in a matrix of sulfated nanofibrillar cellulose (SNFC) and Nafion. The high negative charge densities of the SNFC and Nafion ionomers enhance the cationic selectivity of the composite. The composite is characterized by scanning electron (SEM) and transmission electron (TEM) microscopies as well as Fourier transform infrared (FTIR) and Raman spectroscopies. Tetrahedral Amorphous Carbon (ta-C) electrodes modified with the composite are investigated as potential dopamine (DA) electrochemical sensors. The composite-modified electrodes show significant selectivity and sensitivity toward DA in the presence of ascorbic acid (AA) and uric acid (UA) in physiologically relevant concentrations. A linear dopamine detection range of 0.05–100 μM with detection limits of 65 nM in PBS and 107 nM in interferent solution was determined using 100 mV/s cyclic voltammetry (CV) measurements. These results highlight the potential of t...
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in situ functionalization of Tetrahedral Amorphous Carbon by filtered cathodic arc deposition
AIP Advances, 2019Co-Authors: Sami Sainio, Niklas Wester, Charles J Titus, Dennis Nordlund, Jari Koskinen, Sang Jun Lee, Tomi LaurilaAbstract:Modification of the surface chemistry of Carbon-based nanomaterials is often necessary in order to embrace their full potential. A wide variety of different post-fabrication treatments, such as acid, oxidizing plasma and heat treatments have been described in the literature. However, their specific effects on the materials surface chemistry is typically only vaguely disclosed. Here we report an in-situ method to functionalize Tetrahedral Amorphous Carbon (ta-C) thin films by introducing high purity oxygen into the vacuum chamber during the film fabrication. Additionally, we analyze and compare the material properties of the resulting thin films to those of nitric acid and oxygen plasma treated as well as those with no treatment at all. Using x-ray absorption spectroscopy (XAS), we show that in-situ functionalizing decreases the sp2 content of the surface and increases the amount of carboxyl-like functionalities. Subsequent oxygen plasma treatment further decreases the sp2 fraction and ketone/aldehyde content as well as increases the amount of carboxyl groups. The same trends are observed with the reference ta-C exposed to oxygen plasma treatment. For both materials, a concentrated nitric acid treatment has only a subtle effect on the surface chemistry. Capitalizing on this knowledge, we can selectively produce materials with higher surface loading of specific functional groups, paving the way for application specific material fabrication.
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in situ functionalization of Tetrahedral Amorphous Carbon by filtered cathodic arc deposition
AIP Advances, 2019Co-Authors: Sami Sainio, Niklas Wester, Charles J Titus, Dennis Nordlund, Jari Koskinen, Tomi LaurilaAbstract:Modification of the surface chemistry of Carbon-based nanomaterials is often necessary in order to embrace their full potential. A wide variety of different post-fabrication treatments, such as acid, oxidizing plasma and heat treatments have been described in the literature. However, their specific effects on the materials surface chemistry is typically only vaguely disclosed. Here we report an in-situ method to functionalize Tetrahedral Amorphous Carbon (ta-C) thin films by introducing high purity oxygen into the vacuum chamber during the film fabrication. Additionally, we analyze and compare the material properties of the resulting thin films to those of nitric acid and oxygen plasma treated as well as those with no treatment at all. Using x-ray absorption spectroscopy (XAS), we show that in-situ functionalizing decreases the sp2 content of the surface and increases the amount of carboxyl-like functionalities. Subsequent oxygen plasma treatment further decreases the sp2 fraction and ketone/aldehyde content as well as increases the amount of carboxyl groups. The same trends are observed with the reference ta-C exposed to oxygen plasma treatment. For both materials, a concentrated nitric acid treatment has only a subtle effect on the surface chemistry. Capitalizing on this knowledge, we can selectively produce materials with higher surface loading of specific functional groups, paving the way for application specific material fabrication.Modification of the surface chemistry of Carbon-based nanomaterials is often necessary in order to embrace their full potential. A wide variety of different post-fabrication treatments, such as acid, oxidizing plasma and heat treatments have been described in the literature. However, their specific effects on the materials surface chemistry is typically only vaguely disclosed. Here we report an in-situ method to functionalize Tetrahedral Amorphous Carbon (ta-C) thin films by introducing high purity oxygen into the vacuum chamber during the film fabrication. Additionally, we analyze and compare the material properties of the resulting thin films to those of nitric acid and oxygen plasma treated as well as those with no treatment at all. Using x-ray absorption spectroscopy (XAS), we show that in-situ functionalizing decreases the sp2 content of the surface and increases the amount of carboxyl-like functionalities. Subsequent oxygen plasma treatment further decreases the sp2 fraction and ketone/aldehyde cont...
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computational surface chemistry of Tetrahedral Amorphous Carbon by combining machine learning and density functional theory
Chemistry of Materials, 2018Co-Authors: Volker L Deringer, Tomi Laurila, Miguel A Caro, Gabor Csanyi, Richard Jana, Anja Aarva, S R Elliott, Lars PastewkaAbstract:Tetrahedral Amorphous Carbon (ta-C) is widely used for coatings because of its superior mechanical properties and has been suggested as an electrode material for detecting biomolecules. Despite extensive research, however, the complex atomic-scale structures and chemical reactivity of ta-C surfaces are incompletely understood. Here, we combine machine learning, density functional tight binding, and density functional theory simulations to shed new light on this long-standing problem. We make atomistic models of ta-C surfaces, characterize them by local structural fingerprints, and provide a library of structures at different system sizes. We then move beyond the pure element and exemplify how chemical reactivity (hydrogenation and oxidation) can be modeled at the surfaces. Our work opens up new perspectives for modeling the surfaces and interfaces of Amorphous solids, which will advance studies of ta-C and other functional materials.
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growth mechanism and origin of high sp3 content in Tetrahedral Amorphous Carbon
Physical Review Letters, 2018Co-Authors: Miguel A Caro, Jari Koskinen, Tomi Laurila, Volker L Deringer, Gabor CsanyiAbstract:We study the deposition of Tetrahedral Amorphous Carbon (ta-C) films from molecular dynamics simulations based on a machine-learned interatomic potential trained from density-functional theory data. For the first time, the high sp^{3} fractions in excess of 85% observed experimentally are reproduced by means of computational simulation, and the deposition energy dependence of the film's characteristics is also accurately described. High confidence in the potential and direct access to the atomic interactions allow us to infer the microscopic growth mechanism in this material. While the widespread view is that ta-C grows by "subplantation," we show that the so-called "peening" model is actually the dominant mechanism responsible for the high sp^{3} content. We show that pressure waves lead to bond rearrangement away from the impact site of the incident ion, and high sp^{3} fractions arise from a delicate balance of transitions between three- and fourfold coordinated Carbon atoms. These results open the door for a microscopic understanding of Carbon nanostructure formation with an unprecedented level of predictive power.
Jari Koskinen - One of the best experts on this subject based on the ideXlab platform.
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multiwalled Carbon nanotubes nanofibrillar cellulose nafion composite modified Tetrahedral Amorphous Carbon electrodes for selective dopamine detection
Journal of Physical Chemistry C, 2019Co-Authors: Vasuki Durairaj, Niklas Wester, Tomi Laurila, Jarkko Etula, Janika Lehtonen, Orlando J Rojas, Nikolaos Pahimanolis, Jari KoskinenAbstract:We introduce a composite membrane comprised of multiwalled Carbon nanotubes (MWCNTs) dispersed in a matrix of sulfated nanofibrillar cellulose (SNFC) and Nafion. The high negative charge densities of the SNFC and Nafion ionomers enhance the cationic selectivity of the composite. The composite is characterized by scanning electron (SEM) and transmission electron (TEM) microscopies as well as Fourier transform infrared (FTIR) and Raman spectroscopies. Tetrahedral Amorphous Carbon (ta-C) electrodes modified with the composite are investigated as potential dopamine (DA) electrochemical sensors. The composite-modified electrodes show significant selectivity and sensitivity toward DA in the presence of ascorbic acid (AA) and uric acid (UA) in physiologically relevant concentrations. A linear dopamine detection range of 0.05–100 μM with detection limits of 65 nM in PBS and 107 nM in interferent solution was determined using 100 mV/s cyclic voltammetry (CV) measurements. These results highlight the potential of t...
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in situ functionalization of Tetrahedral Amorphous Carbon by filtered cathodic arc deposition
AIP Advances, 2019Co-Authors: Sami Sainio, Niklas Wester, Charles J Titus, Dennis Nordlund, Jari Koskinen, Sang Jun Lee, Tomi LaurilaAbstract:Modification of the surface chemistry of Carbon-based nanomaterials is often necessary in order to embrace their full potential. A wide variety of different post-fabrication treatments, such as acid, oxidizing plasma and heat treatments have been described in the literature. However, their specific effects on the materials surface chemistry is typically only vaguely disclosed. Here we report an in-situ method to functionalize Tetrahedral Amorphous Carbon (ta-C) thin films by introducing high purity oxygen into the vacuum chamber during the film fabrication. Additionally, we analyze and compare the material properties of the resulting thin films to those of nitric acid and oxygen plasma treated as well as those with no treatment at all. Using x-ray absorption spectroscopy (XAS), we show that in-situ functionalizing decreases the sp2 content of the surface and increases the amount of carboxyl-like functionalities. Subsequent oxygen plasma treatment further decreases the sp2 fraction and ketone/aldehyde content as well as increases the amount of carboxyl groups. The same trends are observed with the reference ta-C exposed to oxygen plasma treatment. For both materials, a concentrated nitric acid treatment has only a subtle effect on the surface chemistry. Capitalizing on this knowledge, we can selectively produce materials with higher surface loading of specific functional groups, paving the way for application specific material fabrication.
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in situ functionalization of Tetrahedral Amorphous Carbon by filtered cathodic arc deposition
AIP Advances, 2019Co-Authors: Sami Sainio, Niklas Wester, Charles J Titus, Dennis Nordlund, Jari Koskinen, Tomi LaurilaAbstract:Modification of the surface chemistry of Carbon-based nanomaterials is often necessary in order to embrace their full potential. A wide variety of different post-fabrication treatments, such as acid, oxidizing plasma and heat treatments have been described in the literature. However, their specific effects on the materials surface chemistry is typically only vaguely disclosed. Here we report an in-situ method to functionalize Tetrahedral Amorphous Carbon (ta-C) thin films by introducing high purity oxygen into the vacuum chamber during the film fabrication. Additionally, we analyze and compare the material properties of the resulting thin films to those of nitric acid and oxygen plasma treated as well as those with no treatment at all. Using x-ray absorption spectroscopy (XAS), we show that in-situ functionalizing decreases the sp2 content of the surface and increases the amount of carboxyl-like functionalities. Subsequent oxygen plasma treatment further decreases the sp2 fraction and ketone/aldehyde content as well as increases the amount of carboxyl groups. The same trends are observed with the reference ta-C exposed to oxygen plasma treatment. For both materials, a concentrated nitric acid treatment has only a subtle effect on the surface chemistry. Capitalizing on this knowledge, we can selectively produce materials with higher surface loading of specific functional groups, paving the way for application specific material fabrication.Modification of the surface chemistry of Carbon-based nanomaterials is often necessary in order to embrace their full potential. A wide variety of different post-fabrication treatments, such as acid, oxidizing plasma and heat treatments have been described in the literature. However, their specific effects on the materials surface chemistry is typically only vaguely disclosed. Here we report an in-situ method to functionalize Tetrahedral Amorphous Carbon (ta-C) thin films by introducing high purity oxygen into the vacuum chamber during the film fabrication. Additionally, we analyze and compare the material properties of the resulting thin films to those of nitric acid and oxygen plasma treated as well as those with no treatment at all. Using x-ray absorption spectroscopy (XAS), we show that in-situ functionalizing decreases the sp2 content of the surface and increases the amount of carboxyl-like functionalities. Subsequent oxygen plasma treatment further decreases the sp2 fraction and ketone/aldehyde cont...
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growth mechanism and origin of high sp3 content in Tetrahedral Amorphous Carbon
Physical Review Letters, 2018Co-Authors: Miguel A Caro, Jari Koskinen, Tomi Laurila, Volker L Deringer, Gabor CsanyiAbstract:We study the deposition of Tetrahedral Amorphous Carbon (ta-C) films from molecular dynamics simulations based on a machine-learned interatomic potential trained from density-functional theory data. For the first time, the high sp^{3} fractions in excess of 85% observed experimentally are reproduced by means of computational simulation, and the deposition energy dependence of the film's characteristics is also accurately described. High confidence in the potential and direct access to the atomic interactions allow us to infer the microscopic growth mechanism in this material. While the widespread view is that ta-C grows by "subplantation," we show that the so-called "peening" model is actually the dominant mechanism responsible for the high sp^{3} content. We show that pressure waves lead to bond rearrangement away from the impact site of the incident ion, and high sp^{3} fractions arise from a delicate balance of transitions between three- and fourfold coordinated Carbon atoms. These results open the door for a microscopic understanding of Carbon nanostructure formation with an unprecedented level of predictive power.
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growth mechanism and origin of high sp 3 content in Tetrahedral Amorphous Carbon
Physical Review Letters, 2018Co-Authors: Miguel A Caro, Jari Koskinen, Tomi Laurila, Volker L Deringer, Gabor CsanyiAbstract:We study the deposition of Tetrahedral Amorphous Carbon (ta-C) films from molecular dynamics simulations based on a machine-learned interatomic potential trained from density-functional theory data. For the first time, the high sp^{3} fractions in excess of 85% observed experimentally are reproduced by means of computational simulation, and the deposition energy dependence of the film's characteristics is also accurately described. High confidence in the potential and direct access to the atomic interactions allow us to infer the microscopic growth mechanism in this material. While the widespread view is that ta-C grows by "subplantation," we show that the so-called "peening" model is actually the dominant mechanism responsible for the high sp^{3} content. We show that pressure waves lead to bond rearrangement away from the impact site of the incident ion, and high sp^{3} fractions arise from a delicate balance of transitions between three- and fourfold coordinated Carbon atoms. These results open the door for a microscopic understanding of Carbon nanostructure formation with an unprecedented level of predictive power.
G A J Amaratunga - One of the best experts on this subject based on the ideXlab platform.
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evolution of sp2 bonding with deposition temperature in Tetrahedral Amorphous Carbon studied by raman spectroscopy
Applied Physics Letters, 2000Co-Authors: Manishkumar Chhowalla, Andrea Ferrari, J Robertson, G A J AmaratungaAbstract:Two transitions in the bonding are found in Tetrahedral Amorphous Carbon (ta-C) films as a function of deposition temperature. The total sp3 fraction shows a sharp decrease at a transition temperature of order 250 °C. In contrast, visible Raman finds that the sp2 sites show a gradual ordering into the graphitic clusters through the sharp bonding transition. The optical gap and resistivity show a similar, gradual transition. This indicates that the sp2 cluster size determines the optical gap, even when the sp2 content does not change. The Raman I(D)/I(G) peak ratio is found to vary inversely with the square of the gap.
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growth mechanism and cross sectional structure of Tetrahedral Amorphous Carbon thin films
Physical Review Letters, 1998Co-Authors: C A Davis, G A J Amaratunga, Kevin M KnowlesAbstract:Spatially resolved electron energy loss spectroscopy is used to characterize the cross-sectional structure of highly Tetrahedral Amorphous Carbon films, particularly concentrating on the ${\mathrm{sp}}^{2}$ bonded surface layer. The surface layer is shown to be due to subsurface conversion from ${\mathrm{sp}}^{2}$ to ${\mathrm{sp}}^{3}$ bonding at the depth of Carbon ion implantation during film growth. The thickness of the surface layer is used as a measure of the ion penetration depth, varying from $0.4\ifmmode\pm\else\textpm\fi{}0.2\mathrm{nm}$ for 35 eV ions to $1.3\ifmmode\pm\else\textpm\fi{}0.3\mathrm{nm}$ for 320 eV ions. The influence of growth temperature is investigated, and it is found that the temperature above which ${\mathrm{sp}}^{3}$ bonding is not stable is greatly reduced in the region affected by ion bombardment.
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highly Tetrahedral Amorphous Carbon films with low stress
Applied Physics Letters, 1996Co-Authors: Manishkumar Chhowalla, G A J Amaratunga, D R Mckenzie, Yongbai Yin, Th FrauenheimAbstract:We have deposited boronated highly Tetrahedral Amorphous Carbon (ta‐C:B) films with low stress using a filtered cathodic vacuum arc. The sp3 fraction, hardness, and resistivity were measured as a function of the ion energy and were found to reach a maximum above 50 eV for B concentrations of 2% and 4%. The most significant result we found was that highly Tetrahedral a‐C:B film (sp3≊80%) with low stress (1–3 GPa) with B concentrations up to 4% could be obtained. The B in the films was found to be predominantly (≊75%) sp2 bonded. Additionally, the stress in the films did not vary with the ion energy or sp3 fraction unlike in regular ta‐C films.
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cross sectional structure of Tetrahedral Amorphous Carbon thin films
Surface & Coatings Technology, 1995Co-Authors: C A Davis, Kevin M Knowles, G A J AmaratungaAbstract:Abstract A cross-sectional transmission electron microscope study of the low density layers at the surface and at the substrate-film interface of Tetrahedral Amorphous Carbon (ta-C) films grown on (001) silicon substrates is presented. Spatially resolved electron energy loss spectroscopy is used to determine the bonding and composition of a Tetrahedral Amorphous Carbon film with nanometre spatial resolution. For a ta-C film grown with a substrate bias of − 300 V, an interfacial region approximately 5 nm wide is present in which the Carbon is sp 2 bonded and is mixed with silicon and oxygen from the substrate. An sp 2 bonded layer observed at the surface of the film is 1.3 ± 0.3 nm thick and contains no detectable impurities. It is argued that the sp 2 bonded surface layer is intrinsic to the growth process, but that the sp 2 bonding in the interfacial layer at the substrate may be related to the presence of oxygen from the substrate.
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deposition of smooth Tetrahedral Amorphous Carbon thin films using a cathodic arc without a macroparticle filter
Applied Physics Letters, 1995Co-Authors: Manishkumar Chhowalla, G A J Amaratunga, M Weiler, C A Davis, B KleinsorgeAbstract:It is shown that for a cathode consisting of compressed graphite powder, the cathodic arc discharge is confined within deep erosion holes and the macroparticle emission is greatly reduced. Electron energy loss spectroscopy and scanning electron microscopy show that smooth Tetrahedral Amorphous Carbon films with up to 85±10% sp3 bonding can be deposited without the use of magnetic filters. The new Carbon arc discharge process holds potential for deposition of smooth Tetrahedral Amorphous Carbon films on large area substrates due to the elimination of the magnetic filtering stage.
J Robertson - One of the best experts on this subject based on the ideXlab platform.
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roughness evolution during growth of hydrogenated Tetrahedral Amorphous Carbon
Diamond and Related Materials, 2006Co-Authors: Simone Pisana, Andrea Ferrari, Cinzia Casiraghi, J RobertsonAbstract:Abstract Hydrogenated Tetrahedral Amorphous Carbon (ta-C:H) is advantageous as coating material for high-density magnetic and optical storage devices, due to its favorable combination of density and smoothness. An advantage of ta-C:H over Tetrahedral Amorphous Carbon (ta-C) is the absence of macroparticles, often found in cathodic arc deposition of ta-C, and the hydrogen rich surface, compatible with the lubricant. As for ta-C, in order to increase the magnetic storage density, the ta-C:H thickness needs to be decreased. It is thus necessary to determine the minimum thickness for continuous and pin-hole free films. Here we investigate the roughness evolution of ta-C:H by atomic force microscopy and determine the roughness and growth exponents α and β . We find a very similar behaviour to ta-C, with the ta-C:H roughness slightly higher than the ta-C one for any given thickness. This confirms the smoothing effect of impinging ions during ta-C:H deposition.
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the smoothness of Tetrahedral Amorphous Carbon
Diamond and Related Materials, 2005Co-Authors: Cinzia Casiraghi, A C Ferrari, J RobertsonAbstract:Abstract Diamond-like Carbon (DLC) is the preferred coating material for magnetic storage disks and future optical storage devices. Tetrahedral Amorphous Carbon (ta-C) films are used to coat the read heads. Films with a thickness below 2 nm and roughness well below 1 nm are needed to achieve the desired storage densities. To reach these values, we must determine the minimum thickness for continuous and pin-hole free films. Here, we review the studies on the smoothness and the growth mechanism of ta-C. The film roughness R of every growing surface generally increases with the thickness z as R ∼ z β until saturation. For a fixed thickness, R increases with the lateral scale length L as R ∼ L α . The exponents α and β are called roughness and growth exponents, respectively, and they are uniquely defined by the growth process. The roughness evolution of ta-C films grown at room temperature was measured by atomic force microscopy. The roughness is very low (∼0.12 nm) and the growth exponents are α ∼0.39 and β ∼0–0.1. These require the presence of surface diffusion and relaxation. We propose that the diffusion is local and it occurs during the thermal spike, which accompanies ion dominated depositions. Monte Carlo simulations confirm this and show low exponents consistent with experiments. Thus, the scaling analysis shows that the surface properties, for a fixed temperature and ion energy, are a separate process to subplantation, which determines the sp 3 bonding of the bulk film.
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surface properties of ultra thin Tetrahedral Amorphous Carbon films for magnetic storage technology
Diamond and Related Materials, 2004Co-Authors: Cinzia Casiraghi, A C Ferrari, R Ohr, Daping Chu, J RobertsonAbstract:Abstract Diamond-like Carbon (DLC) films form a critical protective layer on magnetic hard disks and their reading heads. Film thickness below 2 nm and roughness well below 1 nm are needed for storage density of 200 Gbit/inch 2 . We use atomic force microscopy to study the roughness evolution vs. thickness of highly sp 3 hydrogen-free Tetrahedral Amorphous Carbon (ta-C). The roughness of films r generally follows fractal scaling laws, increasing with film thickness h as r = ah β , where β is the growth exponent. For a fixed film thickness and scan length l , the roughness varies as l α , where α is the roughness exponent. We find α∼0.39 and β∼0–0.1. We performed Monte Carlo simulations, modelling the smoothing effects caused by the thermal spike. The simulation results closely match the experimental findings and define a new growth mechanism for ta-C films. The structural evolution of these ultra-thin films is monitored by Raman spectroscopy. A linear relation between G-peak dispersion and Young's modulus is found. The 2-nm-thick ta-C films are pin-hole free, corrosion resistant, have a Young's Modulus of ∼100 GPa, sp 3 content of ∼50% and roughness of ∼0.12 nm. So, data storage density of 1 Tbit/inch 2 could be achieved.
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dynamic roughening of Tetrahedral Amorphous Carbon
Physical Review Letters, 2003Co-Authors: Cinzia Casiraghi, A C Ferrari, R Ohr, A J Flewitt, Daping Chu, J RobertsonAbstract:The evolution of the surface roughness of growing thin films of metals or semiconductors provides much information about their growth mechanism. Some systems show stages of nucleation, coalescence, and growth. Some systems show microstructures that vary with the growth temperature and conditions [1]. Others show a self-affine behavior in which the roughness varies in a fractal manner with the film thickness and the measurement scale [2 ‐6]. In this case, the randomness of the incident flux creates roughness, which is smoothed by the presence of surface diffusion or surface relaxation and a minimization of surface energy. It is found that the roughness evolution belongs to certain classes depending on the dominant process. These processes are thermally activated, so the observed behavior class depends on the temperature scaled to the melting point — homologous temperature, � —for a given class of materials. This Letter presents the first measurement of the roughness evolution of a highly sp 3 form of Amorphous diamondlike Carbon called Tetrahedral Amorphous Carbon (ta-C) grown from energetic ions [7]. It is found to have an extremely small roughness, of � 0: 1n mroot mean square (rms), and an extremely small growth exponent, and to have these at very low homologous temperatures, of order 0.07, based on a melting point of 4000 K [8]. These results indicate that surface relaxation is occurring at very low scaled temperatures. We interpret this as a smoothening that occurs during a local surface melting caused by the incident ions. This is very important technologically, as the remarkable smoothness of ta-C allows it to form pinhole-free films of only 1‐2 nm thickness, and to act as a protective layer on read heads and disks in magnetic disk storage systems [9]. While the traditional Carbon coatings for magnetic storage cease to protect below 3‐ 4 nm [10], 1‐2 nm thick ta-C films could be used to achieve recording densities over � 100 Gbit=in: 2 and � 1 Tbit=in: 2 for longitudinal and
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effect of graphitic inclusions on the optical gap of Tetrahedral Amorphous Carbon films
Journal of Applied Physics, 2001Co-Authors: Kbk Teo, Sandra E. Rodil, Jeff T. H. Tsai, J Robertson, A C Ferrari, W I MilneAbstract:High sp3 fraction Tetrahedral Amorphous Carbon (ta-C) films can be prepared using the filtered cathodic vacuum arc (FCVA). A by-product of the deposition process are small micrometer sized graphitic particles which are also incorporated into the film. The particle coverage of FCVA films is typically <5%, and thus the effect of these graphite inclusions have been largely ignored in earlier optical gap measurements of ta-C. By incorporating a better filter design (e.g., S-bend filter), the particle coverage can be reduced to 0.1%. In this article, we show that the effect of these graphitic inclusions is to scatter or absorb light which significantly affects the optical gap measurement and hence reduces the “apparent” optical gap of the ta-C film. By comparing two ta-C films with different particle coverage but the same sp3 content of 85%, we show that we can correct for the effect of these inclusions. Our results confirm that the E04 gap of a 85% sp3ta-C matrix is 3.6 eV. The importance of considering these...
D R Mckenzie - One of the best experts on this subject based on the ideXlab platform.
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synthesis of highly Tetrahedral Amorphous Carbon by mixed mode hipims sputtering
Journal of Physics D, 2015Co-Authors: R Ganesan, N A Marks, D G Mcculloch, M D Tucker, J G Partridge, M M M Bilek, D R MckenzieAbstract:Tetrahedral Amorphous Carbon films with an sp 3 content of 80% have been produced by high power impulse magnetron sputtering (HiPIMS) operating in a mixed sputtering/arc mode. In this mode, short-lived cathode spots form in the magnetic racetrack and produce large numbers of Carbon ions. The spots move rapidly, inhibiting the formation of macroparticles. An argon pressure below 2.5 mTorr was critical for obtaining films with high sp 3 content, high stress, large Tauc gap and symmetrical Raman spectra, and all four quantities were strongly correlated.
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nonvolatile memory effects in nitrogen doped Tetrahedral Amorphous Carbon thin films
Journal of Applied Physics, 1998Co-Authors: Ed Gerstner, D R MckenzieAbstract:Electrical measurements of nitrogen doped Tetrahedral Amorphous Carbon (ta-C:N) thin films have revealed a reversible nonvolatile memory effect, related to the excitation and de-excitation of electrons between deep acceptor states and shallow donor states within the mobility gap. This effect is characterized by changes in the small signal film conductivity of up to 10 times, and has been used to fabricate 1-bit memory cells with effective memory retention times in the order of several months.
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highly Tetrahedral Amorphous Carbon films with low stress
Applied Physics Letters, 1996Co-Authors: Manishkumar Chhowalla, G A J Amaratunga, D R Mckenzie, Yongbai Yin, Th FrauenheimAbstract:We have deposited boronated highly Tetrahedral Amorphous Carbon (ta‐C:B) films with low stress using a filtered cathodic vacuum arc. The sp3 fraction, hardness, and resistivity were measured as a function of the ion energy and were found to reach a maximum above 50 eV for B concentrations of 2% and 4%. The most significant result we found was that highly Tetrahedral a‐C:B film (sp3≊80%) with low stress (1–3 GPa) with B concentrations up to 4% could be obtained. The B in the films was found to be predominantly (≊75%) sp2 bonded. Additionally, the stress in the films did not vary with the ion energy or sp3 fraction unlike in regular ta‐C films.
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microscopic structure of Tetrahedral Amorphous Carbon
Physical Review Letters, 1996Co-Authors: N A Marks, D R Mckenzie, Bernard A Pailthorpe, M Bernasconi, Michele ParrinelloAbstract:Simulations are reported of a highly Tetrahedral Amorphous Carbon network at a density of 3 g/cc using Car-Parrinello first principles molecular dynamics. The simulated structure consists of 65% fourfold and 35% threefold coordinated Carbon sites, in good agreement with experiment. The structure is also in good agreement with recent neutron diffraction data. An unexpected observation was the presence of small Carbon rings in the structure containing as few as three atoms. These Carbon triangles and quadrilaterals, which resemble the organic compounds cyclopropane and cyclobutane, give the network a topology unique among Tetrahedrally bonded Amorphous materials.
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ion implantation in Tetrahedral Amorphous Carbon
Physical Review B, 1995Co-Authors: D G Mcculloch, D R Mckenzie, Ed Gerstner, S Prawer, R KalishAbstract:Tetrahedral Amorphous Carbon (ta-C) is a dense form of Amorphous Carbon with a structure consisting of a highly Tetrahedral bonding network. Approximately 20% of the atoms in ta-C are ${\mathit{sp}}^{2}$ hybridized and the presence of these sites plays an important role in the electrical and optical properties of the material. In the present investigation, we use 50 keV ${\mathrm{C}}^{+}$ and 200 keV ${\mathrm{Xe}}^{+}$ ion implantation to damage the structure in a controlled manner. The structure of the ta-C following ion irradiation is monitored using the dose dependence of the electrical conductivity, Raman spectroscopy, electron diffraction, and electron energy-loss spectroscopy. It is shown that the damage is predominantly reflected in an increased concentration of ${\mathit{sp}}^{2}$-bonded sites. With increasing dose, the structure is observed to change from an essentially Tetrahedral network containing ${\mathit{sp}}^{2}$ sites as ``defects'' to an essentially ${\mathit{sp}}^{2}$-bonded structure in which there is a high degree of in-plane disorder combined with a regular stacking of the planes.
