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  • 1
    Electronic Resource
    Electronic Resource
    Low energy ion assisted control of interfacial structure: Ion fluence effects (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 5737-5743 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Multilayered thin films consisting of high electrical conductivity copper layers sandwiched between pairs of low coercivity ferromagnetic alloys can exhibit giant magnetoresistance. The magnitude of the magnetoresistance increases with the structural and chemical perfection of the interfaces. Recent atomistic modeling and experimental observations have shown that nickel and cobalt atoms in the ferromagnetic layer readily exchange with underlying copper atoms during the deposition of the ferromagnetic layer upon the copper spacer. This results in mixing at the ferromagnetic metal on copper interface. Low energy (1–20 eV) inert gas ions can be used during deposition to flatten the surface of layers, in some cases without causing interlayer mixing. Here we use the molecular dynamics simulation method to investigate the effects of the assisting ion fluence upon the surface roughness and interlayer mixing of a model Ni/Cu/Ni multilayer system. The results reveal that the surface roughness initially drops rapidly with ion fluence and then approaches a limiting roughness that is dependent upon the surface type, the ion energy, and the ion mass. For a Cu on Ni surface irradiated by 2.0 eV Xe+ ions, the flattening transition occurs at a fluence of about 0.2 ions/Å2 (corresponding to an ion to metal deposition flux ratio of about 5). The same transition was seen at a similar fluence for a Ni on Cu surface, but at a higher Xe+ ion energy of 14.0 eV. Threshold energies for flattening and mixing were identified for various surfaces. The probabilities of both flattening and mixing were found to increase with ion fluence and ion energy. Because the threshold energy for mixing was lower than that for smoothing, significant interfacial mixing was only seen during ion assisted flattening of the Ni on Cu interface. Simple models have been developed to establish the functional dependence of interfacial structural parameters upon the assisting ion fluence. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1316055
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  • 2
    Electronic Resource
    Electronic Resource
    Atomistic simulation of the vapor deposition of Ni/Cu/Ni multilayers: Incident adatom angle effects (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 553-563 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Molecular dynamics simulations have been used to explore the effects of incident adatom angle upon the atomic scale structure of Ni/Cu/Ni multilayers grown by vapor deposition under controlled incident atom energy conditions. For incident atom energies of 1 eV or less, increasing the incident angle increased interfacial roughness, resulted in void formation in the nickel layer, and intermixing at the interfaces between metal layers. The interfacial roughness that formed during low impact energy oblique angle deposition was significantly reduced by substrate rotation during growth. However, rotation had no beneficial effects upon interfacial mixing. The use of a higher incident atom energy (≥5 eV/atom) resulted in flatter interfaces and eliminated voids under oblique incidence conditions, but it also caused more severe interfacial mixing by an atomic exchange mechanism. When low (thermal) impact energies were used to deposit the first few monolayers of each new metal layer, intermixing by the exchange mechanism during subsequent hyperthermal energy deposition could be significantly reduced. Using this modulated incident energy growth strategy, films with little interfacial roughness and intermixing could be grown over a wide range of incident angles with or without substrate rotation. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371899
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  • 3
    Electronic Resource
    Electronic Resource
    The low energy ion assisted control of interfacial structure: Ion incident energy effects (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 8487-8496 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The properties of multilayered materials are often dependent upon their interfacial structure. For low temperature deposition processes where the structure is kinetically controlled, the interfacial roughness and the extent of interlayer mixing are primarily controlled by the adatom energy used in the deposition. Inert gas ion assistance during the growth process also enables manipulation of the interfacial roughness and intermixing. To explore inert gas ion assistance, a molecular dynamics approach has been used to investigate the role of ion energy and ion species upon the flattening of various surfaces formed during the growth of the Ni/Cu/Ni multilayers. The results indicated that ion energies in the 1–4 eV range could flatten the "rough" copper islands on either copper or nickel crystals. To flatten the rough nickel islands on copper or nickel crystals, higher ion energies in the 9–15 eV range would have to be used. Significant mixing between nickel island atoms and the underlying copper crystal atoms started to occur as the ion energy was increased to around 6–9 eV. However, little mixing was observed between the copper island atoms and the underlying nickel crystal atoms in the same ion energy range. At a given ion energy, the heavier (xenon) ions were found to produce more surface flattening and mixing than the lighter (argon) ions. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373568
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  • 4
    Electronic Resource
    Electronic Resource
    Mechanisms of inert gas impact induced interlayer mixing in metal multilayers grown by sputter deposition (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 3359-3366 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Control of interfacial roughness and chemical mixing is critical in nanomaterials. For example, multilayers composed of ∼20 Å conductive layer sandwiched between two ∼50 Å ferromagnetic layers can exhibit giant magnetoresistance (GMR). This property has caused a tremendous recent increase in hard disk storage capacity, and can potentially result in a new generation of nonvolatile magnetic random access memories. It has been established that good GMR properties can be obtained when the interfacial roughness and interlayer mixing of these multilayers are low. However, flat interfaces in nanoscale multilayers are not thermodynamically stable, and cannot be obtained using thermal energy deposition processes such as molecular-beam epitaxy. Hyperthermal energy sputter deposition techniques using either plasma or ion-beam gun are able to create nonequilibrium flat interfaces, and have been shown to produce better GMR multilayers. In these processes, however, inert gas ions or neutrals with energies between 50 and 200 eV can impact the growth surface. This may be a major source for interlayer mixing. By using a molecular dynamics technique and a reduced order model, the composition profile across the thickness of multiply repeated Ni/Cu/Ni multilayers has been calculated as a function of the energy and the relative flux of the inert gas ions or neutrals as well as the layer thickness. The results indicate that the 50–200 eV inert gas impact caused atomic exchange between adjacent atomic layers near the surface. The probability of exchange increased with impact energy, but decreased with the number of overlayers. The exchange between Ni overlayer and Cu underlayer atoms was much more significant than that between Cu overlayer and Ni underlayer atoms. As a result, the Ni on Cu interfaces were much more diffuse than the Cu on Ni interfaces, in good agreement with experiments. At very high inert gas flux and impact energy, an increased probability for the underlying Cu atoms to be exchanged to the surface resulted in significant Cu surface segregation. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1398073
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  • 5
    Electronic Resource
    Electronic Resource
    Atomistic simulations of the vapor deposition of Ni/Cu/Ni multilayers: The effects of adatom incident energy (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 2301-2315 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Vapor deposited multilayers consisting of a low electrical resistivity conductor sandwiched between ferromagnetic metals such as cobalt or nickel-iron alloys sometimes exhibit giant magnetoresistance (GMR). The GMR properties of these films are a sensitive function of structure and defects in the films and therefore depend upon the processing conditions used for their synthesis. A three-dimensional molecular dynamics method has been developed to simulate the [111] growth of model Ni/Cu/Ni multilayers and was used to investigate the role of vapor atom impact energy upon the film structure and defects. High incident atom energies were found to lower interfacial roughness but promoted intermixing by an atomic exchange mechanism. Low incident energies reduced intermixing, but resulted in films with rough, defective interfaces. The simulations identified an intermediate incident energy between 1 and 2 eV that resulted in both low roughness and intermixing, and an anticipated large GMR effect. The simulation methodology was extended to explore the benefits of a modulated incident atom energy deposition strategy. When a thermal energy was used to deposit the first few monolayers of each new metal layer, intermixing by the exchange mechanism during subsequent hyperthermal energy deposition could be eliminated, and films with almost no interfacial roughness or intermixing could be grown. The modulated energy deposition method can be simply implemented using ion beam deposition. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368297
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  • 6
    Electronic Resource
    Electronic Resource
    Atomistic simulations of low energy ion assisted vapor deposition of metal multilayers (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 2273-2281 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The properties of giant magnetoresistance multilayers are a sensitive function of the vapor deposition process used for their synthesis. The highest magnetoresistance occurs when deposition results in interfaces that are flat and chemically separated. Molecular dynamics simulations have been used to explore the potential benefits of low energy xenon ion assistance during the physical vapor deposition of Ni/Cu/Ni multilayers grown in the [111] direction from thermalized metal fluxes characteristic of molecular beam epitaxy. The simulations indicated that the roughness of the interfaces was significantly reduced as the ion energy was increased from 0 to 5 eV. However, increasing the ion energy above 2 eV also resulted in significant copper–nickel intermixing at the nickel on copper interface. Interface flattening without intermixing could be achieved using a modulated low energy ion assistance strategy in which the first half of each new material layer was deposited without ion assistance, while the remainder of the layer was deposited with an optimum low ion energy assistance of 4 eV. Modulated low energy ion assistance during thermalized metal atom deposition was found to be a promising approach for creating metal multilayers with improved magnetoresistance. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372172
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  • 7
    Electronic Resource
    Electronic Resource
    Tensile testing and TEM analysis of nitrogen-strengthened Fe-Ni-Cr single crystals (1996)
    Springer
    Journal of materials science 31 (1996), S. 5373-5383 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A conventional “abnormal grain growth annealing” heat treatment has been used to produce low (0.009 wt%) and high (0.12 wt%) nitrogen single crystalline Fe-40Ni-15Cr wt% base alloys. Constant strain-rate tensile tests were carried out in the temperature range between 77 and 298 K at two different strain-rates. The results obtained were analysed using the standard procedure for the thermally activated glide of dislocations, and the possible rate-controlling mechanisms for athermal and thermal nitrogen-induced strengthening have been discussed. A conventional two-beam bright-field transmission electron microscope was next used to determine the character of the dislocations and their dependence on the amount of nitrogen in the alloy. It was found that the dislocations became predominantly screw in character as the nitrogen content in the alloy was increased. These findings have been discussed in the light of the existing models for the nitrogen strengthening of the Fe-Ni-Cr austenite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01159306
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  • 8
    Electronic Resource
    Electronic Resource
    Effects of Oxodiperoxovanadate (V) Complexes on the Activity of Green Crab (Scylla serrata) Alkaline Phosphatase (2000)
    Springer
    Biochemistry (Moscow) 65 (2000), S. 1424-1428 
    Details
    ISSN: 1608-3040
    Keywords: alkaline phosphatase ; oxodiperoxovanadate ; inhibition ; inactivation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Green crab (Scylla serrata) alkaline phosphatase (EC 3.1.3.1) is a metalloenzyme that catalyzes the nonspecific hydrolysis of phosphate monoesters. The effects of some pollutants in seawater on the activity of the enzyme will result in the loss of the biological function of the enzyme, which will affect the exuviating crab shell and threaten the survival of the animal. In the present paper, the effects of four oxodiperoxovanadate (V) complexes on the activity of green crab alkaline phosphatase have been studied. The results show that these vanadate derivatives can lead to reversible inactivation. The equilibrium constants for binding of inhibitors with the enzyme and/or the enzyme–substrate complexes have been determined. The results show that sodium (2,2'-bipyridine)oxodiperoxovanadate, pV(bipy), and potassium oxodiperoxo-(1,10-phenanthroline)vanadate, pV(phen), are competitive inhibitors, while potassium picolinato-oxodiperoxo-vanadate, pV(pic), and oxalato-oxodiperoxovanadate, pV(ox), are mixed-type inhibitors. These results suggest that pV(bipy) is a considerably more potent competitive inhibitor than pV(phen) and that the competitive inhibition effect of pV(pic) is stronger than that of pV(ox), but the non-competitive inhibition effect of pV(ox) is stronger than that of pV(pic).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002813125201
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