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Search Results: 1 - 10 of 525338 matches for " G. M. Reuther "
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Characteristics of austenitic stainless steel nitrided in a hybrid glow discharge plasma
Oliveira, R. M.;Ueda, M.;Silva, L. L. G.;Reuther, H.;Lepienski, C. M.;
Brazilian Journal of Physics , 2009, DOI: 10.1590/S0103-97332009000500008
Abstract: a nitriding process based on two distinct nitrogen glow discharge modes, with sample temperatures ranging from 380 0c to 480 0c, was employed to treat the surface of austenitic stainless steel (ss 304). the temperature is controlled exclusively by switching the operation conditions of the discharges. first mode of operation is the conventional one, named cathodic, which runs at higher pressure values (1 mbar) in comparison to the second mode, named anodic, which runs at the pressure range of 10-3 - 10-2 mbar. cathodic mode is used to quickly heat the sample holder, by the high ion flux. on the other hand, in the anodic mode, due to the lower operation pressure, higher effective ion acceleration takes place, which allows deeper ion implantation into the sample surface. this hybrid process was thoroughly explored regarding the duty cycle and conditions of operation, to achieve optimal performance of the treatments, which led to the attainment of surface hardness for samples of aisi ss 304 as high as 20 gpa and improvements including higher elastic modulus and resistance against corrosion. detailed comparison among samples treated by this process with others treated by conventional method was done using nanoindentation, auger electron spectroscopy (aes) and corrosion resistance testing.
Chromium recoil implantation into SAE 1020 steel by nitrogen ion bombardment
Gomes, G. F.;Ueda, M.;Reuther, H.;Richter, E.;Beloto, A. F.;
Brazilian Journal of Physics , 2004, DOI: 10.1590/S0103-97332004000800022
Abstract: sae 1020 is a widely used plain carbon steel, as mortar reinforcement in buildings and small machine parts. but aside from good mechanical properties, its surface suffer from severe corrosion and high wear rate, due to modest hardness. chromium (cr) in excess of 12% in fe alloys renders them resistant to several corrosive attacks. so we tried to introduce cr in such amounts into the surface of that steel. cr films were deposited by electron beam on sae 1020 steel. bombarding the cr film either by nitrogen plasma immersion ion implantation (piii) or nitrogen ion beam (ib), cr atoms were recoil introduced into the fe matrix. normally, in the recoil process, heavy atoms are used, but in this set of experiments we used a relatively lighter atom, viz. nitrogen. srim simulation was used to show cr atoms range in the steel matrix after being hit by nitrogen atoms. aes analysis showed ranges far beyond the calculated figures and in percentages above 13at. %, enough to the purposes of these works. preliminary corrosion results showed remarkable enhancement under corrosive attack.
Creation and manipulation of entanglement in spin chains far from equilibrium
F. Galve,D. Zueco,G. M. Reuther,S. Kohler,P. H?nggi
Physics , 2010, DOI: 10.1140/epjst/e2010-01220-5
Abstract: We investigate creation, manipulation, and steering of entanglement in spin chains from the viewpoint of quantum communication between distant parties. We demonstrate how global parametric driving of the spin-spin coupling and/or local time-dependent Zeeman fields produce a large amount of entanglement between the first and the last spin of the chain. This occurs whenever the driving frequency meets a resonance condition, identified as "entanglement resonance". Our approach marks a promising step towards an efficient quantum state transfer or teleportation in solid state system. Following the reasoning of Zueco et al. [1], we propose generation and routing of multipartite entangled states by use of symmetric tree-like structures of spin chains. Furthermore, we study the effect of decoherence on the resulting spin entanglement between the corresponding terminal spins.
Suppression of secondary phase formation in Fe implanted ZnO single crystals
K. Potzger,Shengqiang Zhou,H. Reuther,K. Kuepper,G. Talut,M. Helm,J. Fassbender,J. D. Denlinger
Physics , 2009, DOI: 10.1063/1.2768196
Abstract: Unwanted secondary phases are one of the major problems in diluted magnetic semiconductor creation. Here, the authors show possibilities to avoid such phases in Fe implanted and postannealed ZnO(0001) single crystals. While -Fe nanoparticles are formed after such doping in as-polished crystals, high temperature (1273 K) annealing in O2 or high vacuum before implantation suppresses these phases. Thus, the residual saturation magnetization in the preannealed ZnO single crystals is about 20 times lower than for the as-polished ones and assigned to indirect coupling between isolated Fe ions rather than to clusters.
Crystallographically oriented magnetic ZnFe2O4 nanoparticles synthesized by Fe implantation into ZnO
Shengqiang Zhou,K. Potzger,H. Reuther,G. Talut,F. Eichhorn,J. von Borany,W. Skorupa,M. Helm,J. Fassbender
Physics , 2006, DOI: 10.1088/0022-3727/40/4/007
Abstract: In this paper, a correlation between structural and magnetic properties of Fe implanted ZnO is presented. High fluence Fe^+ implantation into ZnO leads to the formation of superparamagnetic alpha-Fe nanoparticles. High vacuum annealing at 823 K results in the growth of alpha-Fe particles, but the annealing at 1073 K oxidized the majority of the Fe nanoparticles. After a long term annealing at 1073 K, crystallographically oriented ZnFe2O4 nanoparticles were formed inside ZnO with the orientation relationship of ZnFe2O4(111)[110]//ZnO(0001)[1120]. These ZnFe2O4 nanoparticles show a hysteretic behavior upon magnetization reversal at 5 K.
Results from experiments on hybrid plasma immersion ion implantation/nitriding processing of materials
Ueda, M.;Gomes, G. F.;Kostov, K. G.;Reuther, H.;Lepienski, C. M.;Soares Jr, P. C.;Takai, O.;Silva, M. M.;
Brazilian Journal of Physics , 2004, DOI: 10.1590/S0103-97332004000800023
Abstract: to improve the performance of critical part components, new methods for surface strengthening are being developed with success, like plasma immersion ion implantation (piii) and hybrid surface treatments mixing piii and ion nitriding processes. a combination of high pressure (4 × 101pa), moderate temperature (up to 450oc) glow discharge nitriding with low pressure (8 × 10-2pa) and low dc bias voltage ion nitriding (or dc piii) was implemented. depending on the particular conditions of the treatment and the depth probed, mixed phases of gn and e were measured in the treated ss304 steel sample. this near surface modification resulted in an improved hardness (up to a factor of 2.7 ×) of the sample which could also enhance its wear properties. surface modification of ti6al4v alloy and ss304 steel by a combination of piii and subsequent ion nitriding was investigated as well. nitrogen ions were implanted into the specimens at 15 kev and then ion nitrided at low pressure (7 × 10-2pa) with a bias of -800 v. compared to the untreated samples, the hardness of ti6al4v alloy and the steels could be improved significantly. aes results indicated high retained doses in both samples, confirming the high efficiency of this hybrid process.
Fe-implanted ZnO: Magnetic precipitates versus dilution
Shengqiang Zhou,K. Potzger,G. Talut,H. Reuther,J. von Borany,R. Groetzschel,W. Skorupa,M. Helm,J. Fassbender,N. Volbers,M. Lorenz,T. Herrmannsdoerfer
Physics , 2009, DOI: 10.1063/1.2828060
Abstract: Nowadays ferromagnetism is often found in potential diluted magnetic semiconductor systems. However, many authors argue that the observed ferromagnetism stems from ferromagnetic precipitates or spinodal decomposition rather than from carrier mediated magnetic impurities, as required for a diluted magnetic semiconductor. In the present paper we answer this question for Fe-implanted ZnO single crystals comprehensively. Different implantation fluences and temperatures and post-implantation annealing temperatures have been chosen in order to evaluate the structural and magnetic properties over a wide range of parameters. Three different regimes with respect to the Fe concentration and the process temperature are found: 1) Disperse Fe$^{2+}$ and Fe$^{3+}$ at low Fe concentrations and low processing temperatures, 2) FeZn$_2$O$_4$ at very high processing temperatures and 3) an intermediate regime with a co-existence of metallic Fe (Fe$^0$) and ionic Fe (Fe$^{2+}$ and Fe$^{3+}$). Ferromagnetism is only observed in the latter two cases, where inverted ZnFe$_2$O$_4$ and $\alpha$-Fe nanocrystals are the origin of the observed ferromagnetic behavior, respectively. The ionic Fe in the last case could contribute to a carrier mediated coupling. However, their separation is too large to couple ferromagnetically due to the lack of p-type carrier. For comparison investigations of Fe-implanted epitaxial ZnO thin films are presented.
Ferromagnetism and suppression of metallic clusters in Fe implanted ZnO - a phenomenon related to defects?
Shengqiang Zhou,K. Potzger,G. Talut,H. Reuther,K. Kuepper,J. Grenzer,Qingyu Xu,A. Muecklich M. Helm,J. Fassbender,E. Arenholz
Physics , 2009, DOI: 10.1088/0022-3727/41/10/105011
Abstract: We investigated ZnO(0001) single crystals annealed in high vacuum with respect to their magnetic properties and cluster formation tendency after implant-doping with Fe. While metallic Fe cluster formation is suppressed, no evidence for the relevance of the Fe magnetic moment for the observed ferromagnetism was found. The latter along with the cluster suppression is discussed with respect to defects in the ZnO host matrix, since the crystalline quality of the substrates was lowered due to the preparation as observed by x-ray diffraction.
Effect of He-ion irradiation on Fe-Cr alloys: M?ssbauer - effect study
S. M. Dubiel,J. Cieslak,H. Reuther
Physics , 2012, DOI: 10.1016/j.nucmat.2012.10.048
Abstract: Effect of He ion irradiation on three model Fe(100-x)Cr(x) alloys (x =5.8, 10.75 and 15.15) was investigated with the conversion electron M\"ossbauer spectroscopy. The study of the alloys irradiated with 25 keV ions revealed that the strongest effect occured in the Fe(84.85)Cr(15.15) sample where an inversion of a short-range-order (SRO) parameter was found. Consequently, the investigation of the influence of the irradiation dose, D, was carried out on the chromium-most concentrated sample showing that the average hyperfine field, , the average angle between the normal to the sample's surface and the magnetization vector, , as well as the actual distribution of Fe/Cr atoms, as expressed by SRO parameters, strongly depend on D. In particular: (a) increases with D, and its maximum increase corresponds to a decrease of Cr content within the two-shell volume around the probe 57Fe nuclei by ~2.3 at%, decreases by ~13 degree at maximum, (c) SRO-parameter averaged over the two-shell volume increases with D from weakly negative value (indicative of Cr atoms clustering) to weakly positive value (indicative of Cr atoms ordering). The inversion takes place at D ca. 7 dpa.
Results of an Initial Field Survey for Otters (Lutra lutra) in Jordan
Reuther C.,Rifai L.,Quarcas M.,Baker M.A.
IUCN Otter Specialist Group Bulletin , 2000,
Abstract: An initial field survey for signs of the Eurasian otter, in accordance with the 'Standard Method', was carried out between September and October 2000 in four of the eight permanent watercourses of Jordan. At 7 of the 13 sites surveyed, signs (spraints, footprints) of the otter were found. The results indicate that at least the Rivers Yarmuk and Jordan host an otter population over most of those stretches forming the borders to Syria, Israel, and Palestine. The importance of this population is discussed in the light of its position at the southeastern border of the Mediterranean-Arab range of the Eurasian otter. First agreements for further activities to study the ecology of the otter in this area are introduced.
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