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Sökning: WFRF:(Schmidt Susann)

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1.
  • Anastasopoulos, M., et al. (författare)
  • Multi-Grid detector for neutron spectroscopy : Results obtained on time-of-flight spectrometer CNCS
  • 2017
  • Ingår i: Journal of Instrumentation. - : IOP PUBLISHING LTD. - 1748-0221. ; 12:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The Multi-Grid detector technology has evolved from the proof-of-principle and characterisation stages. Here we report on the performance of the Multi-Grid detector, the MG.CNCS prototype, which has been installed and tested at the Cold Neutron Chopper Spectrometer, CNCS at SNS. This has allowed a side-by-side comparison to the performance of 3He detectors on an operational instrument. The demonstrator has an active area of 0.2 m2. It is specifically tailored to the specifications of CNCS. The detector was installed in June 2016 and has operated since then, collecting neutron scattering data in parallel to the He-3 detectors of CNCS. In this paper, we present a comprehensive analysis of this data, in particular on instrument energy resolution, rate capability, background and relative efficiency. Stability, gamma-ray and fast neutron sensitivity have also been investigated. The effect of scattering in the detector components has been measured and provides input to comparison for Monte Carlo simulations. All data is presented in comparison to that measured by the 3He detectors simultaneously, showing that all features recorded by one detector are also recorded by the other. The energy resolution matches closely. We find that the Multi-Grid is able to match the data collected by 3He, and see an indication of a considerable advantage in the count rate capability. Based on these results, we are confident that the Multi-Grid detector will be capable of producing high quality scientific data on chopper spectrometers utilising the unprecedented neutron flux of the ESS.
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2.
  • Schmidt, Susann, et al. (författare)
  • Boron-10 lined RPCs for sub-millimeter resolution thermal neutron detectors : Feasibility study in a thermal neutron beam
  • 2019
  • Ingår i: Journal of Instrumentation. - : IOP PUBLISHING LTD. - 1748-0221. ; 14:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The results of an experimental feasibility study of a position sensitive thermal neutron detector based on a resistive plate chamber (RPC) are presented. The detector prototype features a thin-gap (0.35 mm) hybrid RPC with an aluminium cathode and a float glass anode. The cathode is lined with a 2 mu m thick (B4C)-B-10 neutron converter enriched in B-10. A detection efficiency of 6.2% is measured at the neutron beam (lambda = 2.5 angstrom) for normal incidence. A spatial resolution better than 0.5 mm FWHM is demonstrated.
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3.
  • Ahmad, Mohammed Metwally Gomaa, et al. (författare)
  • Effect of precursor solutions on the structural and optical properties of sprayed NiO thin films
  • 2017
  • Ingår i: Materials Science in Semiconductor Processing. - : Elsevier BV. - 1369-8001 .- 1873-4081. ; 64, s. 32-38
  • Tidskriftsartikel (refereegranskat)abstract
    • Nickel oxide thin films were deposited by a simple and low-cost spray pyrolysis technique using three different precursors: nickel nitrate, nickel chloride, and nickel acetate on corning glass substrates. X-ray diffraction show that the NiO films are polycrystalline and have a cubic crystal structure, although predominantly with a preferred 111-orientation in the growth direction and a random in-plane orientation. The deconvolution of the Ni 2p and O 1s core level X-ray photoelectron-spectra of nickel oxides produced by using different precursors indicates a shift of the binding energies. The sprayed NiO deposited from nickel nitrate has an optical transmittance in the range of 60-65% in the visible region. The optical band gap energies of the sprayed NiO films deposited from nickel nitrate, nickel chloride and nickel acetate are 3.5, 3.2 and 3.43 eV respectively. Also, the extinction coefficient and refractive index of NiO films have been calculated from transmittance and reflectance measurements. The average value of refractive index for sprayed films by nickel nitrate, nickel chloride and nickel acetate are 2.1, 1.6 and 1.85 respectively. It is revealed that the band gap and refractive index of NiO films by using nickel nitrate corresponds to the commonly reported values. We attribute the observed behavior in the optical band gap and optical constants as due to the change of the Ni/O ratio.
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4.
  • Bakoglidis, Konstantinos, et al. (författare)
  • Comparative study of macro- and microtribological properties of carbon nitride thin films deposited by HiPIMS
  • 2017
  • Ingår i: Wear. - : ELSEVIER SCIENCE SA. - 0043-1648 .- 1873-2577. ; 370
  • Tidskriftsartikel (refereegranskat)abstract
    • The macro- and microtribological properties of carbon nitride thin films deposited by high power impulse magnetron sputtering at different substrate bias voltages (V-b) were investigated. V-b of -100, -150, -200, and-300 V were used. A Hysitron Triboindenter TI950 and a reciprocating Tribotechnic tribometer with diamond counterparts were used in order to assess the tribological performance of the films at the micro- and macroscale, respectively. Initial Hertzian contact pressures of 2.5 GPa, 3.3 GPa and 3.9 GPa were chosen for the comparative measurements at both scales. At the macroscale, films with higher initial roughness present an increased wear. Debris creation and asperity deformation takes place causing abrasive wear. At the microscale, compression of the surface material occurs. The run-in friction shows similar trends at both scales; an initial decrease and an increase thereafter. Steady-state friction is not reached at the microscale, attributed to the absence of a graphitic tribolayer in the contact. At the macroscale, all films show abrasive wear and debris creation. Here, the changes in friction coefficients are attributed to the debris loss from the contact during the tribotests. The CN film tested at 2.5 GPa shows a continuous increase of friction, due to the continuous loss of debris from the contact. The other films reach a steady-state friction coefficient, since most of the debris is lost before the end of the tribotests. (C) 2016 Elsevier B.V. All rights reserved.
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5.
  • Bakoglidis, Konstantinos D., 1985- (författare)
  • Low Friction and Wear Resistant Carbon Nitride Thin Films for Rolling Components Grown by Magnetron Sputtering
  • 2015
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The scope of this licentiate thesis is the investigation of carbon based thin films suitable for rolling components, especially roller bearings. Carbon and carbon nitride are materials with advantageous tribological properties and high resiliency. Such materials are required in order to withstand the demanding conditions of bearing operation, such as high loads and corrosive environments. A fundamental condition for coated bearings is that the deposition temperature must be striktly limited. Thus, carbon nitride (CNx) thin films were synthesized here at low temperature of 150 oC by different reactive magnetron sputtering techniques, which are mid-frequency magnetron sputtering (MFMS), direct current magnetron sputtering (DCMS), and high power impulse magnetron sputtering (HiPIMS). While DCMS is a very well studied technique for carbon based films, MFMS and HiPIMS are relatively new sputtering techniques for carbon, and especially CNx depositions. Using different magnetron sputtering techniques, different ionization conditions prevail in the chamber during each process and influence the obtained film properties at a great extent. It was found that bias duty cycles and the amount of working gas ions are key parameters and affect the morphology and microstructure as well as the mechanical response of the films. Moreover, different bias voltages, from 20 V up to 120 V were applied during the processes in order to investigate the changes that the different ion energies induce in the film structure.The structural, mechanical and tribological properties of CNx films are also presented in this licentiate thesis. The morphology of CNx films strongly depends on both the deposition technique and ion energy. The special configuration of MFMS mode produces highly homogeneous and dense films even from low applied bias voltages, while in HiPIMS mode high bias voltages above 100 V must be applied in order to produce films with similar structural characteristics. DCMS is also proven as a good technique for homogeneous and dense films. Low bias voltages do not favor  homogeneous structures, thus at 20 V all techniques produced films with columnar structures with intercolumnar voids. High bias voltages influence the N incorporation in the films, with the appearance of re-sputtering of N-containing species and a promotion of sp2 bonding configurations with increasing ion energy. Nevertheless, the different deposition mode influences the sp2 content in different ways, with only MFMS showing a clear increase of sp2 content with increasing bias voltage and HiPIMS showing relatively constant sp2 content. The morphology and microstructure of the CNx films affects their mechanical response, with higher ion energies producing harder films. A dependency of hardness and elastic modulus with increasing ion energy was obtained, where for all deposition modes, hardness and elastic modulus increase linearly with increasing bias voltage. Films with hardness as high as 25 GPa were synthesized by MFMS at 120 V , while the softer film yielded a hardness of 7 GPa and was deposited by HiPIMS at 20 V . The elastic recovery of the films differs with increasing ion energies, presenting a correlation with the C sp2 bond content. The highest elastic recovery of 90% was extracted for the film deposited by MFMS at 120 V and is a value similar to the elastic recovery obtained for FL-CNx films. All films developed compressive residual stresses, depending also on the ion energies and the deposition mode used. It is demonstrated that the induced stresses in the films increase when denser and more homogeneous film morphologies are obtained and with higher Ar intercalcation. Low friction coefficients were obtained for all films between 0.05 and 0.07, although the deposition conditions are not detrimental for the development of friction coefficient. The wear resistance of the films was found to be dependent on the morphology and to some extent on the microstructure of the films. Harder, denser, and more homogeneous films have higher wear resistance. Especially, CNx films deposited by MFMS at 120 V present no wear.The tribological characteristics of the surface of the films were also investigated at nanoscale by a new reciprocal wear test. In this wear test, the recording of the track profile is performed in between consecutive test cycles, eliminating also thermal drift. The very low wear of the films deposited by MFMS at 100 V and 120 V revealed that during the wear test a phase transformation on the surface may take place, possibly graphitization. It is also demonstrated the way that the surface characteristics, such as asperities and roughness affects the tribological measurements. Attention is also turned to the presence of large asperities on the film surface and the way they affect the obtained average friction coefficient and tribological measured data.
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6.
  • Bakoglidis, Konstantinos D., et al. (författare)
  • Low-temperature growth of low friction wear-resistant amorphous carbon nitride thin films by mid-frequency, high power impulse, and direct current magnetron sputtering
  • 2015
  • Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 33:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Amorphous carbon nitride (a-CNx) thin films were deposited on steel AISI52100 and Si(001) substrates using mid-frequency magnetron sputtering (MFMS) with an MF bias voltage, high power impulse magnetron sputtering (HiPIMS) with a synchronized HiPIMS bias voltage, and direct current magnetron sputtering (DCMS) with a DC bias voltage. The films were deposited at a low substrate temperature of 150 °C and a N2/Ar flow ratio of 0.16 at the total pressure of 400 mPa. The negative bias voltage (Vs) was varied from 20 V to 120 V in each of the three deposition modes. The microstructure of the films was characterized by high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED), while the film morphology was investigated by scanning electron microscopy (SEM). All films possessed amorphous microstructure with clearly developed columns extending throughout the entire film thickness. Layers grown with the lowest substrate bias of 20 V exhibited pronounced intercolumnar porosity, independent of the technique used. Voids closed and dense films formed at Vs ≥ 60 V, Vs ≥ 100 V and Vs = 120 V for MFMS, DCMS and HiPIMS, respectively. X-ray photoelectron spectroscopy (XPS) revealed that the nitrogen-to-carbon ratio, N/C, of the films ranged between 0.2 and 0.24. Elastic recoil detection analysis (ERDA) showed that Ar content varied between 0 and 0.8 at% and increases as a function of Vs for all deposition techniques. All films exhibited compressive residual stress, σ, which depends on the growth method; HiPIMS produces the least stressed films with stress between – 0.4 and – 1.2 GPa for all Vs values, while for CNx films deposited by MFMS σ = – 4.2 GPa. Nanoindentation showed a significant increase in film hardness and reduced elastic modulus with increasing Vs for all techniques. The harder films were produced by MFMS with hardness as high as 25 GPa. Low friction coefficients, between 0.05 and 0.06, were recorded for all films. Furthermore, CNx films produced by MFMS and DCMS at Vs = 100 V and 120 V presented a high wear resistance with wear coefficients of k ≤ 2.3 x 10-5 mm3/Nm.
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7.
  • Bakoglidis, Konstantinos D., et al. (författare)
  • Nanotribological properties of wear resistant a-CNx thin films deposited by mid-frequency magnetron sputtering
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • The nanotribological properties of amorphous carbon nitride (a-CNx) thin films deposited with mid-frequency magnetron sputtering (MFMS) were investigated at the nanoscale using an in-situ technique in a Hysitron Triboindenter TI 950. The friction coefficient, wear rate, track roughness, and the track profiles were recorded as a function of the number of linear reciprocal cycles, revealing the manner that the nanotribological and surface properties change during the wear test. The surface composition of  the films was evaluated by x-ray photoelectron spectroscopy (XPS). The friction coefficient ranges between 0.05 – 0.07, while the wear coefficient ranges from 9.4 x 10-8 up to 1.5 x 10-4 mm3/Nm. Debris particles and surface modifications characterize the friction and lubrication behavior in the track. The friction and main lubrication mechanism on the modified surface changes after the removal of debris particles, while this change appears at different cycle for each CNx film depending on the substrate bias voltage. Films grown at higher bias are modified earlier than films grown at lower bias. The wear behavior can be divided into two, track roughnessdependent, regimes; (1) films with track roughness > 1 nm showed wear with obvious tracks and (2) the films with roughness < 1 nm showed negative wear at the nanometer scale with a volume of material projected in the area of the wear track. This material volume is believed to be result of a surface modification, where the molar volume of the modified surface is larger than the molar volume of the surface before the wear test.
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8.
  • Bakoglidis, Konstantinos, et al. (författare)
  • Improved adhesion of carbon nitride coatings on steel substrates using metal HiPIMS pretreatments
  • 2016
  • Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 302, s. 454-462
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the effect of low-temperature metal pretreatments in order to improve the adhesion of CNx coatings on steel substrates, which is crucial for tribological applications. The substrate pretreatments were conducted using five different metal targets: Ti, Zr, Al, Cr, and W, operated in high power impulse magnetron sputtering mode, known to produce significant ionization of the sputtered material flux. The CNx adhesion, as assessed by Rockwell C tests, did not improve upon Ti and Zr pretreatments. This is primarily ascribed to the fact that no interlayer was formed owing to severe re-sputtering due to high fluxes of doubly-ionized metal species in the plasma. A slight improvement in adhesion was observed in the case an Al pretreatment was carried out, while the best results were obtained using Cr and W. Here, 30-s-long pretreatments were sufficient to clean the steel surface and form a metallic interlayer between substrate and coating. Transmission electron microscopy in combination with energy dispersive X-ray spectroscopy revealed that Al, Cr, and W created intermixing zones at the interlayer/substrate and the interlayer/CNx interfaces. The steel surfaces, pretreated using Cr or W, showed the highest work of adhesion with W-adh(Cr) = 1.77 J/m(2) and W-adh(W) = 1.66 J/m(2), respectively. (C) 2016 Elsevier B.V. All rights reserved.
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9.
  • Bakoglidis, Konstantinos (författare)
  • Low-friction and wear-resistant carbon nitride coatings for bearing components grown by magnetron sputtering
  • 2016
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The scope of this thesis is the investigation of magnetron sputtered carbon nitride coatings suitable for roller bearing components. The research field of tribology of bearings focuses on minimizing friction between components by improving the lubricants. The development of lubricants is, however, expensive and involves environmentally deleterious chemical byproducts. A solution to avoid such harmful conditions, reduce the processing cost, and more importantly, minimize the friction, is to apply a low-friction and wear-resistant coating on the surface of the bearing. The deposition of such coatings on components can substantially increase their lifetime, reduce the maintenance costs, and eventually increase the reliability of the machinery.Carbon nitride (CNx) coatings have high resiliency and can withstand the demanding conditions of bearing operation. The morphology of CNx coatings is highly affected by applying a negative substrate bias voltage. At high bias (100-120 V ), the coatings become denser and more homogeneous with decreased porosity, resulting in more wear-resistant materials. I also found that the duty cycle of the applied bias affects the layer morphology. Less homogeneous films are produced using lower duty cycles (i.e., in high power impulse magnetron sputtering, HiPIMS) for a specific value of bias voltage. Thus, changing bias voltage, we can manipulate the structure of CNx and design layers, depending on the requirements of the bearing application.My results show that denser films yield higher hardness and wear-resistance, but also higher compressive stress, which is a disadvantage for the coating-substrate adhesion. In order to obtain improved adhesion on bearing steel, we developed an in-situ surface treatment, prior to the CNx deposition, which also surpasses the limitations set by the properties of each material. The steel substrates are successfully pretreated using W or Cr ions originating from a HiPIMS source. Plasma ions are accelerated to the substrates with energies of 900 eV , due to the application of a synchronized high bias voltage, which clean effectively the substrate surface from residual contaminants and strengthen the interfacial bonding.CNx-coated rollers are tested in rolling operation and show the absence of run-in period in all lubrication regimes. This is a big advantage for applications which rotate under boundary lubrication (BL). The coated rollers yield friction coefficients in the range of 0:020 and 0:025 in elastohydrodynamic (EHDL) and hydrodynamic (HDL) lubrication regimes, being lower than the friction coefficients of 0:026-0:052, exhibited by the uncoated rollers. Here, friction decreases steadily with increasing number of cycles, due to the presence of CNx in the contact. In BL, CNx-coated rollers present an increased friction coefficient of 0:052, but the wear is much lower than in the case of uncoated rollers. All rollers are covered with CNx in the wear tracks after the tests, avoiding failures and presenting low abrasive wear. The obtained tribological performance of the CNx-coated rollers in rolling is overall improved compared to the established operation of uncoated rollers. Thus, CNx layers can function as low-friction and wear-resistant coatings protecting the steel components in several roller bearing applications, such as in gearboxes and wheels in automotive, aerospace, marine, and turbine industry.
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10.
  • Bakoglidis, Konstantinos, et al. (författare)
  • Rolling contact fatigue of bearing components coated with carbon nitride thin films
  • 2016
  • Ingår i: Tribology International. - : ELSEVIER SCI LTD. - 0301-679X .- 1879-2464. ; 98, s. 100-107
  • Tidskriftsartikel (refereegranskat)abstract
    • Bearing rollers were coated with CNx films using high power impulse magnetron sputtering deposition in order to reduce their rolling-contact fatigue as investigated using a Micro-Pitting Rig tribometer under poly-alpha-olefin lubricated conditions. Coated rollers with a similar to 15 nm thick W adhesion layer to the substrate, exhibit the best performance, presenting mild wear and no fatigue after 700 kcycles. The steady-state friction coefficient was similar to 0.05 for both uncoated and coated rollers. Uncoated rollers show run-in friction in the first 50 kcycles, because of steel-to-steel contact, which is absent for coated rollers. Analytical transmission electron microscopy and X-ray photoelectron spectroscopy show that the presence of a CNx coating prevents steel-to-steel contact of the counterparts, prior to the elastohydrodynamic lubrication, reducing their wear and increasing the lifetime expectancy. (C) 2016 Elsevier Ltd. All rights reserved.
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11.
  • Bakoglidis, Konstantinos, et al. (författare)
  • Rolling performance of carbon nitride-coated bearing components in different lubrication regimes
  • 2017
  • Ingår i: Tribology International. - : Pergamon Press. - 0301-679X .- 1879-2464. ; 114, s. 141-151
  • Tidskriftsartikel (refereegranskat)abstract
    • The performance of carbon nitride (CN) coated roller bearings is investigated, using a micropitting rig. The rolling performance is evaluated using Stribeck test, with a continuously varying rolling speed (0.2 - 2 m/s). Rolling contact fatigue tests with constant speeds (0.5, 1, 2, and 3.5 m/s) are also conducted in order to study the high-cycle performance of the rollers. The obtained Stribeck curve shows that the presence of coatings eliminates run-in, resulting in low friction coefficients (similar to 0.08). Raman spectroscopy, performed at the wear tracks, reveals that CNx maintain stable chemical state. Coatings show abrasion although the wear rate is not detrimental for the performance of the rollers, since a CNx to-steel contact is retained during the entire rolling contact fatigue test.
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13.
  • Filho, Luimar Correa, et al. (författare)
  • The Effect of Coating Density on Functional Properties of SiNx Coated Implants
  • 2019
  • Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 12:20
  • Tidskriftsartikel (refereegranskat)abstract
    • Ceramic coatings may be applied onto metallic components of joint replacements for improved wear and corrosion resistance as well as enhanced biocompatibility, especially for metal-sensitive patients. Silicon nitride (SiNx) coatings have recently been developed for this purpose. To achieve a high coating density, necessary to secure a long-term performance, is however challenging, especially for sputter deposited SiNx coatings, since these coatings are insulating. This study investigates the time-dependent performance of sputter-deposited SiNx based coatings for joint applications. SiNx coatings with a thickness in the range of 4.3–6.0 µm were deposited by reactive high power impulse magnetron sputtering onto flat discs as well as hip heads made of CoCrMo. SiNx compositional analysis by X-ray photoelectron spectroscopy showed N/Si ratios between 0.8 and 1.0. Immersion of the flat disks in fetal bovine serum solution over time as well as short-term wear tests against ultra-high molecular weight polyethylene (UHMWPE) discs showed that a high coating density is required to inhibit tribocorrosion. Coatings that performed best in terms of chemical stability were deposited using a higher target power and process heating.
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15.
  • Filho, Luimar, et al. (författare)
  • The effect of N, C, Cr, and Nb content on silicon nitride coatings for joint applications
  • 2020
  • Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 13:8
  • Tidskriftsartikel (refereegranskat)abstract
    • Ceramic coatings are an alternative to achieve or maintain a high wear resistance of metallic surfaces, and simultaneously allow for a reduction in metal ion release. Silicon nitride based (SiNx) coatings deposited by high power impulse magnetron sputtering (HiPIMS) have shown potential for use in joint implants seen from an improved chemical stability in combination with a good adhesion. The aim of this study was to investigate the effect of N, C, Cr and Nb content on the tribocorrosive performance of 3.7 to 8.8 µm thick SiNx coatings deposited by HiPIMS onto CoCrMo discs to improve  the mechanical properties and/or chemical stability of SiNx .Coating composition was evaluated by X-ray photoelectron spectroscopy (XPS) and the surface roughness by Vertical Scanning Interferometry (VSI). Hardness and Young’s modulus were investigated by nanoindentation and coating adhesion was measured by scratch tests. Multidirectional wear tests against UHMWPE pins were performed for 2 million cycles in bovine serum solution (25%) at 37°C, at an estimated contact pressure of 2.1 MPa.Coatings with a relatively low hardness tended to fail earlier in the wear test, due to chemical reactions and eventually dissolution, accelerated by the tribological contact. In fact, while no definite correlation could be observed between coating composition (N: 42.6-55.5 at%, C: 0-25.7 at%, Cr: 0 or 12.8 at%, and Nb: 0-24.5 at%) and wear performance, it was apparent that high-purity and/or -density coatings (i.e. low oxygen content and high nitrogen content) were desirable to prevent coating and/or counter surface wear. Coatings deposited with a higher energy fulfilled the target profile in terms of low surface roughness (Ra<20nm), adequate adhesion (Lc2>30N), chemical stability over time in the tribocorrosive environment, as well as low polymer wear, presenting potential for a future application in joint bearings.
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16.
  • Filho, Luimar, et al. (författare)
  • Towards Functional Silicon Nitride Coatings for Joint Replacements
  • 2019
  • Ingår i: Coatings. - : MDPI AG. - 2079-6412. ; 9:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Silicon nitride (SiNx) coatings are currently under investigation as bearing surfaces for joint implants, due to their low wear rate and the good biocompatibility of both coatings and their potential wear debris. The aim of this study was to move further towards functional SiNx coatings by evaluating coatings deposited onto CoCrMo surfaces with a CrN interlayer, using different bias voltages and substrate rotations. Reactive direct current magnetron sputtering was used to coat CoCrMo discs with a CrN interlayer, followed by a SiNx top layer, which was deposited by reactive high-power impulse magnetron sputtering. The interlayer was deposited using negative bias voltages ranging between 100 and 900 V, and 1-fold or 3-fold substrate rotation. Scanning electron microscopy showed a dependence of coating morphology on substrate rotation. The N/Si ratio ranged from 1.10 to 1.25, as evaluated by X-ray photoelectron spectroscopy. Vertical scanning interferometry revealed that the coated, unpolished samples had a low average surface roughness between 16 and 33 nm. Rockwell indentations showed improved coating adhesion when a low bias voltage of 100 V was used to deposit the CrN interlayer. Wear tests performed in a reciprocating manner against Si3N4 balls showed specific wear rates lower than, or similar to that of CoCrMo. The study suggests that low negative bias voltages may contribute to a better performance of SiNx coatings in terms of adhesion. The low wear rates found in the current study support further development of silicon nitride-based coatings towards clinical application.
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20.
  • Gharavi, Mohammad Amin, et al. (författare)
  • Microstructure and thermoelectric properties of CrN and CrN/Cr2N thin films
  • 2018
  • Ingår i: Journal of Physics D. - : IOP PUBLISHING LTD. - 0022-3727 .- 1361-6463. ; 51:35
  • Tidskriftsartikel (refereegranskat)abstract
    • CrN thin films with an N/Cr ratio of 95% were deposited by reactive magnetron sputtering onto (0001) sapphire substrates. X-ray diffraction and pole figure texture analysis show CrN (111) epitaxial growth in a twin domain fashion. By changing the nitrogen versus argon gas flow mixture and the deposition temperature, thin films with different surface morphologies ranging from grainy rough textures to flat and smooth films were prepared. These parameters can also affect the CrN(x )system, with the film compound changing between semiconducting CrN and metallic Cr2N through the regulation of the nitrogen content of the gas flow and the deposition temperature at a constant deposition pressure. Thermoelectric measurements (electrical resistivity and Seebeck coefficient), scanning electron microscopy, and transmission electron microscopy imaging confirm the changing electrical resistivity between 0.75 and 300 m omega cm, the changing Seebeck coefficient values between 140 and 230 mu VK-1, and the differences in surface morphology and microstructure as higher temperatures result in lower electrical resistivity while gas flow mixtures with higher nitrogen content result in single phase cubic CrN.
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21.
  • Gonzales-Siles, Lucia, et al. (författare)
  • A Pangenome Approach for Discerning Species-Unique Gene Markers for Identifications of Streptococcus pneumoniae and Streptococcus pseudopneumoniae
  • 2020
  • Ingår i: Frontiers in Cellular and Infection Microbiology. - : Frontiers Media SA. - 2235-2988. ; 10
  • Tidskriftsartikel (refereegranskat)abstract
    • Correct identifications of isolates and strains of the Mitis-Group of the genus Streptococcus are particularly difficult, due to high genetic similarity, resulting from horizontal gene transfer and homologous recombination, and unreliable phenotypic and genotypic biomarkers for differentiating the species. Streptococcus pneumoniae and Streptococcus pseudopneumoniae are the most closely related species of the clade. In this study, publicly-available genome sequences for Streptococcus pneumoniae and S. pseudopneumoniae were analyzed, using a pangenomic approach, to find candidates for species-unique gene markers; ten species-unique genes for S. pneumoniae and nine for S. pseudopneumoniae were identified. These species-unique gene marker candidates were verified by PCR assays for identifying S. pneumoniae and S. pseudopneumoniae strains isolated from clinical samples. All determined species-level unique gene markers for S. pneumoniae were detected in all S. pneumoniae clinical isolates, whereas fewer of the unique S. pseudopneumoniae gene markers were present in more than 95% of the clinical isolates. In parallel, taxonomic identifications of the clinical isolates were confirmed, using conventional optochin sensitivity testing, targeted PCR-detection for the "Xisco" gene, as well as genomic ANIb similarity analyses for the genome sequences of selected strains. Using mass spectrometry-proteomics, species-specific peptide matches were observed for four of the S. pneumoniae gene markers and for three of the S. pseudopneumoniae gene markers. Application of multiple species-level unique biomarkers of S. pneumoniae and S. pseudopneumoniae, is proposed as a protocol for the routine clinical laboratory for improved, reliable differentiation, and identification of these pathogenic and commensal species.
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22.
  • Goyenola, Cecilia, et al. (författare)
  • Carbon Fluoride, CFx: Structural Diversity as Predicted by First Principles
  • 2014
  • Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:12, s. 6514-6521
  • Tidskriftsartikel (refereegranskat)abstract
    • Fluorinated carbon-based thin films offer a wide range of properties for many technological applications that depend on the microstructure of the films. To gain a better understanding of the role of fluorine in the structural formation of these films, CFx systems based on graphene-like fragments were studied by first-principles calculations. Generally, the F concentration determines the type of film that can be obtained. For low F concentrations (up to similar to 5 at. %), films with fullerene-like as well as graphite-like features are expected. Larger F concentrations (greater than= 10 at. %) give rise to increasingly amorphous carbon films. Further increasing the F concentration in the films leads to formation of a polymer-like microstructure. To aid the characterization of CFx systems generated by computational methods, a statistical approach is developed.
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23.
  • Hellgren, Niklas, et al. (författare)
  • Interpretation of X-ray photoelectron spectra of carbon-nitride thin films: New insights from in situ XPS
  • 2016
  • Ingår i: Carbon. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0008-6223 .- 1873-3891. ; 108, s. 242-252
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on angular-resolved x-ray photoelectron spectroscopy (XPS) studies of magnetron sputtered CNx thin films, first in situ (without air exposure), then after air exposure (for time periods ranging from minutes to several years), and finally after Ar ion etching using ion energies ranging from 500 eV to 4 keV. The as-deposited films typically exhibit two strong N1s peaks corresponding to pyridine-like, and graphite-like, at similar to 398.2 eV and similar to 400.7 eV, respectively. Comparison between in situ and air-exposed samples suggests that the peak component at similar to 402-403 eV is due only to quaternary nitrogen and not oxidized nitrogen. Furthermore, peak components in the similar to 399-400 eV range cannot only be ascribed to nitriles or pyrrolic nitrogen as is commonly done. We propose that it can also be due to a polarization shift in pyridinic N, induced by surface water or hydroxides. Argon ion etching readily removes surface oxygen, but results also in a strong preferential sputtering of nitrogen and can cause amorphization of the film surface. The best methods for evaluating and interpreting the CNx film structure and composition with ex-situ XPS are discussed. (C) 2016 Elsevier Ltd. All rights reserved.
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24.
  • Hänninen, Tuomas, 1988-, et al. (författare)
  • Silicon carbonitride thin films deposited by reactive high power impulse magnetron sputtering
  • 2018
  • Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 335, s. 248-256
  • Tidskriftsartikel (refereegranskat)abstract
    • Amorphous silicon carbonitride thin films for biomedical applications were deposited in an industrial coating unit from a silicon target in different argon/nitrogen/acetylene mixtures by reactive high power impulse magnetron sputtering (rHiPIMS). The effects of acetylene (C2H2) flow rate, substrate temperature, substrate bias voltage, and HiPIMS pulse frequency on the film properties were investigated. Low C2H2 flow rates (<10 sccm) resulted in silicon nitride-like film properties, seen from a dense morphology when viewed in cross-sectional scanning electron microscopy, a hardness up to ∼22 GPa as measured by nanoindentation, and Si-N bonds dominating over Si-C bonds in X-ray photoelectron spectroscopy core-level spectra. Higher C2H2 flows resulted in increasingly amorphous carbon-like film properties, with a granular appearance of the film morphology, mass densities below 2 g/cm3 as measured by X-ray reflectivity, and a hardness down to 4.5 GPa. Increasing substrate temperatures and bias voltages resulted in slightly higher film hardnesses and higher compressive residual stresses. The film H/E ratio showed a maximum at film carbon contents ranging between 15 and 30 at.% and at elevated substrate temperatures from 340 °C to 520 °C.
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25.
  • Hänninen, Tuomas, 1988- (författare)
  • Silicon Nitride Based Coatings Grown by Reactive Magnetron Sputtering
  • 2018
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Silicon nitride and silicon nitride-based ceramics have several favorable material properties, such as high hardness and good wear resistance, which makes them important materials for the coating industry. This thesis focuses the synthesis of silicon nitride, silicon oxynitride, and silicon carbonitride thin films by reactive magnetron sputtering. The films were characterized based on their chemical composition, chemical bonding structure, and mechanical properties to link the growth conditions to the film properties. Silicon nitride films were synthesized by reactive high power impulse magnetron sputtering (HiPIMS) from a Si target in Ar/N2 atmospheres, whereas silicon oxynitride films were grown by using nitrous oxide as the reactive gas. Silicon carbonitride was synthesized by two different methods. The first method was using acetylene (C2H2) in addition to N2 in a Si HiPIMS process and the other was co-sputtering of Si and C, using HiPIMS for Si and direct current magnetron sputtering (DCMS) for graphite targets in an Ar/N2 atmosphere. Langmuir probe measurements were carried out for the silicon nitride and silicon oxynitride processes and positive ion mass spectrometry for the silicon nitride processes to gain further understanding on the plasma conditions during film growth. The target current and voltage waveforms of the reactive HiPIMS processes were evaluated.The main deposition parameter affecting the nitrogen concentration of silicon nitride films was found to be the nitrogen content in the plasma. Films with nitrogen contents of 50 at.% were deposited at N2/Ar flow ratios of 0.3 and above. These films showed Si-N as the dominating component in Si 2p X-ray photoelectron spectroscopy (XPS) core level spectra and Si–Si bonds were absent. The substrate temperature and target power were found to affect the nitrogen content to a lower extent. The residual stress and hardness of the films were found to increase with the film nitrogen content. Another factors influencing the coating stress were the process pressure, negative substrate bias, substrate temperature, and HiPIMS pulse energy. Silicon nitride coatings with good adhesion and low levels of compressive residual stress were grown by using a pressure of 600 mPa, a substrate temperature below 200 °C, pulse energies below 2.5 Ws, and negative bias voltages up to 100 V.The elemental composition of silicon oxynitride films was shown to depend on the target power settings as well as on the nitrous oxide flow rate. Silicon oxide-like films were synthesized under poisoned target surface conditions, whereas films deposited in the transition regime between poisoned and metallic conditions showed higher nitrogen concentrations. The nitrogen content of the films deposited in the transition region was controlled by the applied gas flow rate. The applied target power did not affect the nitrogen concentration in the transition regime, while the oxygen content increased at decreasing target powers. The chemical composition of the films was shown to range from silicon-rich to effectively stoichiometric silicon oxynitrides, where no Si–Si contributions were found in the XPS Si 2p core level spectra. The film optical properties, namely the refractive index and extinction coefficient, were shown to depend on the film chemical bonding, with the stoichiometric films displaying optical properties falling between those of silicon oxide and silicon nitride.The properties of silicon carbonitride films were greatly influenced by the synthesis method. The films deposited by HiPIMS using acetylene as the carbon source showed silicon nitride-like mechanical properties, such as a hardness of ~ 20 GPa and compressive residual stresses of 1.7 – 1.9 GPa, up to film carbon contents of 30 at.%. At larger film carbon contents the films had increasingly amorphous carbon-like properties, such as densities below 2 g/cm3 and hardnesses below 10 GPa. The films with more than 30 at.% carbon also showed columnar morphologies in cross-sectional scanning electron microscopy, whereas films with lower carbon content showed dense morphologies. Due to the use of acetylene the carbonitride films contained hydrogen, up to ~ 15 at.%. The co-sputtered silicon carbonitride films showed a layered SiNx/CNx structure. The hardness of these films increased with the film carbon content, reaching a maximum of 18 GPa at a film carbon content of 12 at.%. Comparatively hard and low stressed films were grown by co-sputtering using a C target power of 1200 W for a C content around 12 at.%, a negative substrate bias less than 100 V, and a substrate temperature up to 340 °C.
  •  
26.
  • Hänninen, Tuomas, et al. (författare)
  • Silicon oxynitride films deposited by reactive high power impulse magnetron sputtering using nitrous oxide as a single-source precursor
  • 2015
  • Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : A V S AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 33:5, s. 05E121-
  • Tidskriftsartikel (refereegranskat)abstract
    • Silicon oxynitride thin films were synthesized by reactive high power impulse magnetron sputtering of silicon in argon/nitrous oxide plasmas. Nitrous oxide was employed as a single-source precursor supplying oxygen and nitrogen for the film growth. The films were characterized by elastic recoil detection analysis, x-ray photoelectron spectroscopy, x-ray diffraction, x-ray reflectivity, scanning electron microscopy, and spectroscopic ellipsometry. Results show that the films are silicon rich, amorphous, and exhibit a random chemical bonding structure. The optical properties with the refractive index and the extinction coefficient correlate with the film elemental composition, showing decreasing values with increasing film oxygen and nitrogen content. The total percentage of oxygen and nitrogen in the films is controlled by adjusting the gas flow ratio in the deposition processes. Furthermore, it is shown that the film oxygen-to-nitrogen ratio can be tailored by the high power impulse magnetron sputtering-specific parameters pulse frequency and energy per pulse. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
  •  
27.
  • Hänninen, Tuomas (författare)
  • Silicon Oxynitride Thin Films Grown by Reactive HiPIMS
  • 2015
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Amorphous silicon oxynitride (SiOxNy) thin films were grown by reactive high power impulse magnetron sputtering from a pure silicon target in Ar/N2O plasmas. The elemental composition of the films was shown to depend on the target surface conditions during the film deposition, as well as on the reactive gas flow rate. When the target was sputtered under poisoned surface conditions, the film composition was predominantly silicon oxide, whereas films deposited in the transition regime between poisoned and metallic target surface conditions showed higher nitrogen concentrations, as measured by X-ray photoelectron spectroscopy (XPS) and elastic recoil detection analysis (ERDA). The different target surface conditions were identified based on the evolution of the target current waveforms upon variation of the deposition parameters. The average electron temperatures during the peak target current were determined by Langmuir probe measurements, to assist with the explanation of the observed target current behavior and target poisoning characteristics.The chemical composition of the films was shown to range from silicon-rich to effectively stoichiometric silicon oxynitrides, where no Si–Si contributions were found in the XPS Si 2p core level spectra. The film optical properties, the refractive index n and the extinction coefficient k, were shown to depend on the film chemical bonding, with the effectively stoichiometric films displaying optical properties falling between those of SiO2 and Si3N4.
  •  
28.
  • Hänninen, Tuomas, et al. (författare)
  • Stoichiometric silicon oxynitride thin films reactively sputtered in Ar/N2O plasmas by HiPIMS
  • 2016
  • Ingår i: Journal of Physics D. - : Institute of Physics (IOP). - 0022-3727 .- 1361-6463. ; 49:13
  • Tidskriftsartikel (refereegranskat)abstract
    • Silicon oxynitride (SiOxNy, x = 0.2 − 1.3, y = 0.2 − 0.7) thin films were synthesized by reactive high power impulse magnetron sputtering from a pure silicon target in Ar/N2O atmospheres. It is found that the composition of the material can be controlled by the reactive gas flow and the average target power. X-ray photoelectron spectroscopy (XPS) shows that high average powers result in more silicon-rich films, while lower target powers yield silicon-oxide-like material due to more pronounced target poisoning. The amount of nitrogen in the films can be controlled by the percentage of nitrous oxide in the working gas. The nitrogen content remains at a constant level while the target is operated in the transition region between metallic and poisoned target surface conditions. The extent of target poisoning is gauged by the changes in peak target current under the different deposition conditions. XPS also shows that varying concentrations and ratios of oxygen and nitrogen in the films result in film chemical bonding structures ranging from silicon-rich to stoichiometric silicon oxynitrides having no observable Si−Si bond contributions. Spectroscopic ellipsometry shows that the film optical properties depend on the amount and ratio of oxygen and nitrogen in the compound, with film refractive indices measured at 633 nm ranging between those of SiO2 and Si3N4.
  •  
29.
  • Högberg, Hans, et al. (författare)
  • Reactive sputtering of CSx thin solid films using CS2 as precursor
  • 2020
  • Ingår i: Vacuum. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-207X .- 1879-2715. ; 182
  • Tidskriftsartikel (refereegranskat)abstract
    • We deposit CSx thin solid films by reactive direct current magnetron sputtering of a C target in an argon plasma, using carbon disulfide (CS2) as a precursor to film growth. We investigate the influence of the partial pressure of the CS2 vapor introduced into the plasma on the composition, the chemical bonding structure, the structural, and the mechanical properties as determined by x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, scanning electron microscopy (SEM), and nanoindentation for films deposited at 150 and 300 degrees C. The Raman and the XPS results indicate that S atoms are incorporated in mostly sp(2) bonded C network. These results agree with previous ab-initio theoretical findings obtained by modeling of the CSx compound by the Synthetic Growth Concept. The microstructure of the films as well as the results of their Raman characterization and the nano mechanical testing results all point out that with the increasing S content some spa bonding is admixed in the predominantly sp(2) bonded CSx network, leading to typical amorphous structure with short and interlocked graphene-like planes for S contents between 2% and 8%. We conclude that CSx thin solid films deposited by using CS2 as a precursor would be CSx films deposited at low temperature of similar to 150 degrees C and with an S content in the region of 6 at.% may be interesting candidates for applications as hard/elastic protective coatings.
  •  
30.
  • Imam, Mewlude, et al. (författare)
  • Gas Phase Chemistry of Trimethylboron in Thermal Chemical Vapor Deposition
  • 2017
  • Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:47, s. 26465-26471
  • Tidskriftsartikel (refereegranskat)abstract
    • Alkylboranes, such as trimethylboron (TMB) and triethylboron (TEB), are promising alternative precursors in low temperature chemical vapor deposition (CVD) of boron-containing thin films. In this study, CVD growth of B-C films using TMB and quantum-chemical calculations to elucidate a gas phase chemical mechanism were undertaken. Dense, amorphous, boron-rich (B/C 1.5-3) films were deposited at 1000 degrees C in both dihydrogen and argon ambients, while films with crystalline B4C and B25C inclusions were deposited at 1100 degrees C in dihydrogen. A script-based automatization scheme was implemented for the quantum-chemical computations to enable time efficient screening of thousands of possible gas phase CVD reactions. The quantum-chemical calculations suggest TMB is mainly decomposed by an unimolecular alpha-H elimination of methane, which is complemented by dihydrogen-assisted elimination of methane in dihydrogen.
  •  
31.
  • Imam, Mewlude, et al. (författare)
  • Plasma CVD of hydrogenated boron-carbon thin films from triethylboron
  • 2018
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 148:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Low-temperature chemical vapor deposition (CVD) of B - C thin films is of importance for neutron voltaics and semiconductor technology. The highly reactive trialkylboranes, with alkyl groups of 1-4 carbon atoms, are a class of precursors that have been less explored for low-temperature CVD of B - C films. Herein, we demonstrate plasma CVD of B - C thin films using triethylboron (TEB) as a single source precursor in an Ar plasma. We show that the film density and B/C ratio increases with increasing plasma power, reaching a density of 2.20 g/cm3 and B/C = 1.7. This is attributed to a more intense energetic bombardment during deposition and more complete dissociation of the TEB molecule in the plasma at higher plasma power. The hydrogen content in the films ranges between 14 and 20 at. %. Optical emission spectroscopy of the plasma shows that BH, CH, C2, and H are the optically active plasma species from TEB. We suggest a plasma chemical model based on β-hydrogen elimination of C2H4 to form BH3, in which BH3 and C2H4 are then dehydrogenated to form BH and C2H2. Furthermore, C2H2 decomposes in the plasma to produce C2 and CH, which together with BH and possibly BH3-x(C2H5)x are the film forming species. 
  •  
32.
  • Imam, Mewlude, et al. (författare)
  • Trimethylboron as Single-Source Precursor for Boron-Carbon Thin Film Synthesis by Plasma Chemical Vapor Deposition
  • 2016
  • Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:38, s. 21990-21997
  • Tidskriftsartikel (refereegranskat)abstract
    • Boron carbon (BxC) thin films are potential neutron converting layers for B-10-based neutron detectors. However, as common material choices for such detectors do not tolerate temperatures above 500 degrees C, a low temperature deposition route is required. Here, we study trimethylboron B(CH3)(3) (TMB) as a single-source precursor for the deposition of BxC thin films by plasma CVD using Ar plasma. The effect of plasma power, TMB/Ar flow ratio and total pressure, on the film composition, morphology, chemical bonding, and microstructures are investigated. Dense and boron-rich films (B/C = 1.9) are achieved at high TMB flow under a low total pressure and high plasma power, which rendered an approximate substrate temperature of similar to 300 degrees C. Films mainly contain B-C bonds with the presence of B-O and C-C, which is attributed to be the origin of formed amorphous carbon in the films. The high H content 15 +/- 5 at. %) is almost independent of deposition parameters and contributed to lower the film density (2.16 g/cm(3)). The plasma compositional analysis shows that the TMB molecule decomposes to mainly atomic H, C-2, BH, and CH. A plasma chemical model for the decomposition of TMB with BH and CH as the plausible film depositing species in the plasma is proposed.
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33.
  • Imam, Mewlude, et al. (författare)
  • Trimethylboron as single-source precursor for boron-carbonthin film synthesis by plasma chemical vapor deposition
  • 2015
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Boron-carbon (BxC) thin films are potential neutron converting layers for 10B-based neutron detectors. However, as common material choices for such detectors do not tolerate temperature above 500°C, a low temperature deposition route is required for this application. Here we study trimethylboron B(CH3)3 (TMB) as a single-source precursor for the deposition of BxC thin films by plasma CVD using Ar plasma. The effect of plasma power, TMB/Ar ratio and total pressure on the film composition, morphology and structure are investigated. The highest B/C ratio of 1.9 was achieved at high TMB flow in a low total pressure and high plasma power which rendered an approximate substrate temperature of ~ 300 °C. X-ray photoelectron spectroscopy shows that B-C bonds prevail in the films, although C-C and B-O bonds are also present. Raman spectroscopy confirms the presence of amorphous carbon phases in the films. The H content in the films is found to be 15±5 at. % by the time of flight elastic recoil detection analysis (Tof-ERDA). The film density as determined from X-ray reflectivity (XRR) measurements is 2. 16 ± 0.01  g/cm3 and the internal compressive stresses are measured to be less than 400 MPa.
  •  
34.
  • Kostov Gueorguiev, Gueorgui, et al. (författare)
  • CF(x): A first-principles study of structural patterns arising during synthetic growth
  • 2011
  • Ingår i: Chemical Physics Letters. - : Elsevier. - 0009-2614 .- 1873-4448. ; 516:1-3, s. 62-67
  • Tidskriftsartikel (refereegranskat)abstract
    • Structural and bonding patterns arising from the incorporation of fluorine atoms in a graphene-like network relevant to the deposition of carbon fluoride (CF(x)) films were addressed by first-principles calculations. We find that large N-member (N = 8-12) rings, defects by sheet branching, and defects associated with bond rotation pertain to CF(x). The cohesive energy gains associated with these patterns are similar to 0.2-0.4 eV/at., which is similar to those for a wide range of defects in other C-based nanostructured solids. Fullerene-like CF(x) is predicted for F concentrations below similar to 10 at.%, while CF(x) compounds with higher F content are predominantly amorphous or polymeric.
  •  
35.
  • López, Alejandro, 1983-, et al. (författare)
  • Morphology and adhesion of silicon nitride coatings upon soaking in fetal bovine serum
  • 2018
  • Ingår i: 15th International Symposium on Computer Methods in Biomechanics and Biomedical Engineering and 3rd Conference on Imaging and Visualization, Lisbon, March 26-29, 2018.
  • Konferensbidrag (refereegranskat)abstract
    • Total hip joint replacements are considered successful in providing patients with close- to-normal lives; however, revision surgeries still represent an individual and socioeconomic burden due to wear and failure of the implants, which occurs at a rate of 3-10% at 10 years. Therefore, eorts are being made to increase the lifespan of articial prostheses. Because of the impossibility to avoid wear debris, functional silicon nitride coatings are being developed due their low wearing, particle solubility and good biological response. However, a compromise needs to be found between coating reactivity and durability.A HIPIMS process was used to sputter a CrN interlayer followed by a SiNx top layer using 1- and 3-fold rotation in an industrial deposition system (CemeCon AG, Würselen, Germany). In order to measure the adhesion of the coatings to the cobalt-chromium-molybdenum substrates a scratch test was used, consisting of generating a scratch with a Rockwell C diamond stylus, at an increasing load from 0 to 100 N, at a displacement rate of 6mm/min. The samples were immersed in 25% fetal bovine serum solution to mimic synovial joint uid and scratched aer 0, 1, 3, 6 weeks periods in this solution. The cross-section of the coatings was assessed through Focused Ion Beam at 30kV for milling and 5kV for secondary electron imaging of the surface.The coatings demonstrated a high nitrogen content, previously shown to be benecial in terms of low dissolution rates. The deposition conditions and coating morphology were found to have an eect on the dissolution rate and thereby also the spallation failure of the coatings. These results are informative for the further development of these coatings into parts of functional 3D implants. 
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36.
  •  
37.
  • Magnuson, Martin, 1965-, et al. (författare)
  • Electronic properties and bonding in ZrHx thin films investigated by valence-bandx-ray photoelectron spectroscopy
  • 2017
  • Ingår i: Physical Review B Condensed Matter. - College Park, United States : American Physical Society. - 0163-1829 .- 1095-3795. ; 96:19
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure and chemical bonding in reactively magnetron sputtered ZrHx (x = 0.15, 0.30, 1.16)thin films with oxygen content as low as 0.2 at.% are investigated by 4d valence band, shallow 4p core-level,and 3d core-level x-ray photoelectron spectroscopy. With increasing hydrogen content, we observe significantreduction of the 4d valence states close to the Fermi level as a result of redistribution of intensity toward the H1s–Zr 4d hybridization region at ∼6 eV below the Fermi level. For low hydrogen content (x = 0.15, 0.30), thefilms consist of a superposition of hexagonal closest-packed metal (α phase) and understoichiometric δ-ZrHx(CaF2-type structure) phases, while for x = 1.16, the films form single-phase ZrHx that largely resembles thatof stoichiometric δ-ZrH2 phase. We show that the cubic δ-ZrHx phase is metastable as thin film up to x = 1.16,while for higher H contents the structure is predicted to be tetragonally distorted. For the investigated ZrH1.16film, we find chemical shifts of 0.68 and 0.51 eV toward higher binding energies for the Zr 4p3/2 and 3d5/2peak positions, respectively. Compared to the Zr metal binding energies of 27.26 and 178.87 eV, this signifiesa charge transfer from Zr to H atoms. The change in the electronic structure, spectral line shapes, and chemicalshifts as a function of hydrogen content is discussed in relation to the charge transfer from Zr to H that affectsthe conductivity by charge redistribution in the valence band.
  •  
38.
  • Mauri, G., et al. (författare)
  • Neutron reflectometry with the Multi-Blade B-10-based detector
  • 2018
  • Ingår i: Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences. - : The Royal Society. - 1364-5021 .- 1471-2946. ; 474:2216
  • Tidskriftsartikel (refereegranskat)abstract
    • The Multi-Blade is a boron-10-based gaseous detector developed for neutron reflectometry instruments at the European Spallation Source in Sweden. The main challenges for neutron reflectometry detectors are the instantaneous counting rate and spatial resolution. The Multi-Blade has been tested on the CRISP reflectometer at the ISIS Neutron and Muon Source in the UK. A campaign of scientific measurements has been performed to study the Multi-Blade response in real instrumental conditions. The results of these tests are discussed in this paper.
  •  
39.
  • Moshontz, Hannah, et al. (författare)
  • The Psychological Science Accelerator: Advancing Psychology Through a Distributed Collaborative Network
  • 2018
  • Ingår i: Advances in Methods and Practices in Psychological Science. - : SAGE Publications. - 2515-2459 .- 2515-2467. ; 1:4, s. 501-515
  • Tidskriftsartikel (refereegranskat)abstract
    • Concerns about the veracity of psychological research have been growing. Many findings in psychological science are based on studies with insufficient statistical power and nonrepresentative samples, or may otherwise be limited to specific, ungeneralizable settings or populations. Crowdsourced research, a type of large-scale collaboration in which one or more research projects are conducted across multiple lab sites, offers a pragmatic solution to these and other current methodological challenges. The Psychological Science Accelerator (PSA) is a distributed network of laboratories designed to enable and support crowdsourced research projects. These projects can focus on novel research questions or replicate prior research in large, diverse samples. The PSA’s mission is to accelerate the accumulation of reliable and generalizable evidence in psychological science. Here, we describe the background, structure, principles, procedures, benefits, and challenges of the PSA. In contrast to other crowdsourced research networks, the PSA is ongoing (as opposed to time limited), efficient (in that structures and principles are reused for different projects), decentralized, diverse (in both subjects and researchers), and inclusive (of proposals, contributions, and other relevant input from anyone inside or outside the network). The PSA and other approaches to crowdsourced psychological science will advance understanding of mental processes and behaviors by enabling rigorous research and systematic examination of its generalizability.
  •  
40.
  • Muraro, A., et al. (författare)
  • Neutron radiography as a non-destructive method for diagnosing neutron converters for advanced thermal neutron detectors
  • 2016
  • Ingår i: Journal of Instrumentation. - : Institute of Physics (IOP). - 1748-0221. ; 11:C03033
  • Tidskriftsartikel (refereegranskat)abstract
    • Due to the well-known problem of He-3 shortage, a series of different thermal neutron detectors alternative to helium tubes are being developed, with the goal to find valid candidates for detection systems for the future spallation neutron sources such as the European Spallation Source (ESS). A possible He-3-free detector candidate is a charged particle detector equipped with a three dimensional neutron converter cathode (3D-C). The 3D-C currently under development is composed by a series of alumina (Al2O3) lamellas coated by 1 mu m of B-10 enriched boron carbide (B4C). In order to obtain a good characterization in terms of detector efficiency and uniformity it is crucial to know the thickness, the uniformity and the atomic composition of the B4C neutron converter coating. In this work a non-destructive technique for the characterization of the lamellas that will compose the 3D-C was performed using neutron radiography. The results of these measurements show that the lamellas that will be used have coating uniformity suitable for detector applications. This technique (compared with SEM, EDX, ERDA, XPS) has the advantage of being global (i.e. non point-like) and non-destructive, thus it is suitable as a check method for mass production of the 3D-C elements.
  •  
41.
  • Muraro, Andrea, et al. (författare)
  • Performance of the high-efficiency thermal neutron BAND-GEM detector
  • 2018
  • Ingår i: Progress of Theoretical and Experimental Physics. - : Oxford University Press (OUP). - 2050-3911. ; :2
  • Tidskriftsartikel (refereegranskat)abstract
    • Newhigh-count-rate detectors are required for future spallation neutron sources where large-area and high-efficiency (>50%) detectors are envisaged. In this framework, Gas Electron Multiplier (GEM) is one of the detector technologies being explored, since it features good spatial resolution (<0.5 cm) and timing properties, has excellent rate capability (MHz/mm(2)) and can cover large areas (some m(2)) at low cost. In the BAND-GEM (boron array neutron detector GEM) approach a 3D geometry for the neutron converter cathode was developed that is expected to provide an efficiency >30% in thewavelength range of interest for small angle neutron scattering instruments. A system of aluminum grids with thin walls coated with a 0.59 mu m layer of (B4C)-B-10 has been built and positioned in the first detector gap, orthogonally to the cathode. By tilting the grid system with respect to the beam, there is a significant increase of effective thickness of the borated material crossed by the neutrons. As a consequence, both interaction probability and detection efficiency are increased. This paper presents the results of the performance of the BAND-GEM detector in terms of efficiency and spatial resolution.
  •  
42.
  • Pettersson, Maria, et al. (författare)
  • Dissolution behaviour of silicon nitride coatings for joint replacements
  • 2016
  • Ingår i: Materials science & engineering. C, biomimetic materials, sensors and systems. - : Elsevier BV. - 0928-4931 .- 1873-0191. ; 62, s. 497-505
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, the dissolution rate of SiNx coatings was investigated as a function of coating composition, in comparison to a cobalt chromium molybdenum alloy (CoCrMo) reference. SiNx coatings with N/Si ratios of 03, 0.8 and 1.1 were investigated. Electrochemical measurements were complemented with solution (inductively coupled plasma techniques) and surface analysis (vertical scanning interferometry and x-ray photoelectron spectroscopy). The dissolution rate of the SiNx coatings was evaluated to 0.2-1.4 nm/day, with a trend of lower dissolution rate with higher N/Si atomic ratio in the coating. The dissolution rates of the coatings were similar to or lower than that of CoCrMo (0.7-1.2 nm/day). The highest nitrogen containing coating showed mainly Si-N bonds in the bulk as well as at the surface and in the dissolution area. The lower nitrogen containing coatings showed Si-N and/or Si-Si bonds in the bulk and an increased formation of Si-O bonds at the surface as well as in the dissolution area. The SiNx coatings reduced the metal ion release from the substrate. The possibility to tune the dissolution rate and the ability to prevent release of metal ions encourage further studies on SiNx coatings for joint replacements
  •  
43.
  • Pettersson, Maria, et al. (författare)
  • Mechanical and tribological behavior of silicon nitride and silicon carbon nitride coatings for total joint replacements
  • 2013
  • Ingår i: Journal of The Mechanical Behavior of Biomedical Materials. - : Elsevier BV. - 1751-6161 .- 1878-0180. ; 25, s. 41-47
  • Tidskriftsartikel (refereegranskat)abstract
    • Total joint replacements currently have relatively high success rates at 10-15 years; however, increasing ageing and an active population places higher demands on the longevity of the implants. A wear resistant configuration with wear particles that resorb in vivo can potentially increase the lifetime of an implant. In this study, silicon nitride (SixNy) and silicon carbon nitride (SixCyNz) coatings were produced for this purpose using reactive high power impulse magnetron sputtering (HiPIMS). The coatings are intended for hard bearing surfaces on implants. Hardness and elastic modulus of the coatings were evaluated by nanoindentation, cohesive, and adhesive properties were assessed by micro-scratching and the tribological performance was investigated in a ball-on-disc setup run in a serum solution. The majority of the SixNy coatings showed a hardness close to that of sintered silicon nitride (similar to 18 GPa), and an elastic modulus close to that of cobalt chromium (similar to 200 GPa). Furthermore, all except one of the SixNy coatings offered a wear resistance similar to that of bulk silicon nitride and significantly higher than that of cobalt chromium. In contrast, the SixCyNz coatings did not show as high level of wear resistance. 
  •  
44.
  •  
45.
  • Pettersson, Maria, et al. (författare)
  • Structure and composition of silicon nitride and silicon carbon nitridecoatings for joint replacements
  • 2013
  • Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 235, s. 827-834
  • Tidskriftsartikel (refereegranskat)abstract
    • SiNx and SiCxNy coatings were fabricated with high power impulse magnetron sputtering (HiPIMS). The coatings microstructure, growth pattern, surface morphology, composition, and bonding structure were investigated by AFM, SEM, GIXRD, TEM, EDS as well as XPS, and related to the deposition parameters target powers and substrate temperature. Cross-sections of SiCxNy coatings showed either dense and laminar, or columnar structures. These coatings varied in roughness (Ra between 0.2 and 3.8 nm) and contained up to 35 at.% C. All coatings were substoichiometric (with an N/Si ratio from 0.27 to 0.65) and contained incorporated particles (so called droplets). The SiNx coatings, in particular those deposited at the lower power on the silicon target, demonstrated a dense microstructure and low surface roughness (Ra between 0.2 and 0.3 nm). They were dominated by an (X-ray) amorphous structure and consisted mainly of Si–N bonds. The usefulness of these coatings is discussed for bearing surfaces for hip joint arthroplasty in order to prolong their life-time. The long-term aim is to obtain a coating that reduces wear and metal ion release, that is biocompatible, and with wear debris that can dissolve in vivo.
  •  
46.
  • Pfeiffer, D., et al. (författare)
  • First measurements with new high-resolution gadolinium-GEM neutron detectors
  • 2016
  • Ingår i: Journal of Instrumentation. - : IOP PUBLISHING LTD. - 1748-0221. ; 11
  • Tidskriftsartikel (refereegranskat)abstract
    • European Spallation Source instruments like the macromolecular diffractometer (NMX) require an excellent neutron detection efficiency, high-rate capabilities, time resolution, and an unprecedented spatial resolution in the order of a few hundred micrometers over a wide angular range of the incoming neutrons. For these instruments solid converters in combination with Micro Pattern Gaseous Detectors (MPGDs) are a promising option. A GEM detector with gadolinium converter was tested on a cold neutron beam at the IFE research reactor in Norway. The mu TPC analysis, proven to improve the spatial resolution in the case of B-10 converters, is extended to gadolinium based detectors. For the first time, a Gd-GEM was successfully operated to detect neutrons with a measured efficiency of 11.8% at a wavelength of 2 angstrom and a position resolution better than 250 mu m.
  •  
47.
  • Pietropaolo, A., et al. (författare)
  • Neutron diffraction measurements on a reference metallic sample with a high-efficiency GEM side-on B-10-based thermal neutron detector
  • 2018
  • Ingår i: Europhysics letters. - : IOP PUBLISHING LTD. - 0295-5075 .- 1286-4854. ; 121:6
  • Tidskriftsartikel (refereegranskat)abstract
    • The upgraded version of the GEM side-on thermal neutron detector was successfully tested in a neutron diffraction experiment on a reference sample using the INES diffractometer at the ISIS spallation neutron source, UK. The performance of the new (B4C)-B-10-based detector is compared to that of a standard He-3 tube, operating at the instrument as a part of the detectors assembly. The results show that the upgraded detector has a better resolution and an efficiency of the same order of magnitude of a He-3-based detector. Copyright (C) EPLA, 2018
  •  
48.
  • Piscitelli, F., et al. (författare)
  • Characterization of the Multi-Blade 10B-based detector at the CRISP reflectometer at ISIS for neutron reflectometry at ESS
  • 2018
  • Ingår i: Journal of Instrumentation. - : IOP PUBLISHING LTD. - 1748-0221. ; 13:5
  • Tidskriftsartikel (refereegranskat)abstract
    • The Multi-Blade is a Boron-10-based gaseous thermal neutron detector developed to face the challenge arising in neutron reflectometry at neutron sources. Neutron reflectometers are challenging instruments in terms of instantaneous counting rate and spatial resolution. This detector has been designed according to the requirements given by the reflectometers at the European Spallation Source (ESS) in Sweden. The Multi-Blade has been installed and tested on the CRISP reflectometer at the ISIS neutron and muon source in U.K.. The results on the detailed detector characterization are discussed in this manuscript.
  •  
49.
  • Piscitelli, Francesco, et al. (författare)
  • Neutron reflectometry on highly absorbing films and its application to (B4C)-B-10-based neutron detectors
  • 2016
  • Ingår i: Royal Society of London. Proceedings A. Mathematical, Physical and Engineering Sciences. - : The Royal Society. - 1364-5021 .- 1471-2946. ; 472:2185
  • Tidskriftsartikel (refereegranskat)abstract
    • Neutron reflectometry is a powerful tool used for studies of surfaces and interfaces. The absorption in the typical studied materials is neglected and this technique is limited only to the reflectivity measurement. For strongly absorbing nuclei, the absorption can be directly measured by using the neutron-induced fluorescence technique which exploits the prompt particle emission of absorbing isotopes. This technique is emerging from soft matter and biology where highly absorbing nuclei, in very small quantities, are used as a label for buried layers. Nowadays, the importance of absorbing layers is rapidly increasing, partially because of their application in neutron detection; a field that has become more active also due to the He-3-shortage. We extend the neutron-induced fluorescence technique to the study of layers of highly absorbing materials, in particular (B4C)-B-10. The theory of neutron reflectometry is a commonly studied topic; however, when a strong absorption is present the subtle relationship between the reflection and the absorption of neutrons is not widely known. The theory for a general stack of absorbing layers has been developed and compared to measurements. We also report on the requirements that a (B4C)-B-10 layer must fulfil in order to be employed as a converter in neutron detection.
  •  
50.
  • Piscitelli, F., et al. (författare)
  • The Multi-Blade Boron-10-based neutron detector for high intensity neutron reflectometry at ESS
  • 2017
  • Ingår i: Journal of Instrumentation. - : IOP PUBLISHING LTD. - 1748-0221. ; 12:3
  • Tidskriftsartikel (refereegranskat)abstract
    • The Multi-Blade is a Boron-10-based gaseous detector introduced to face the challenge arising in neutron reflectometry at pulsed neutron sources. Neutron reflectometers are the most challenging instruments in terms of instantaneous counting rate and spatial resolution. This detector has been designed to cope with the requirements set for the reflectometers at the upcoming European Spallation Source (ESS) in Sweden. Based on previous results obtained at the Institut Laue-Langevin (ILL) in France, an improved demonstrator has been built at ESS and tested at the Budapest Neutron Centre (BNC) in Hungary and at the Source Testing Facility (STF) at the Lund University in Sweden. A detailed description of the detector and the results of the tests are discussed in this manuscript.
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