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Digitale Medien

Kinetic and thermochemical study of the silyl + hydrogen bromide .dblharw. silane + bromine atom and silyl + hydrogen iodide .dblharw. silane + iodine atom equilibria (1991)

Seetula, J. A. ; Feng, Y. ; Gutman, D. ; [weitere]

s.l. : American Chemical Society

The @journal of physical chemistry 〈Washington, DC〉 95 (1991), S. 1658-1664

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Quelle: ACS Legacy Archives

Thema: Chemie und Pharmazie , Physik

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1021/j100157a030

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2

Digitale Medien

Spatial variation of the critical current density of the high Tc superconducting thin films (1992)

Feng, Y. J. ; Cheng, Q. H. ; Wu, P. H. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 72 (1992), S. 5350-5353

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Low-temperature scanning electron microscopy (LTSEM) is a promising measuring technique for probing the spatial distribution of the superconducting properties of high Tc thin films. In the presented article we have given some experimental observations on the spatial variation of the critical current density of two kinds of high Tc thin films using a LTSEM. The results show that in the polycrystalline TlBaCaCuO film prepared by dc magnetron sputtering, the maximum local critical current density is about 3–4 times greater than the minimum local critical current density. The microstructure analysis implies that the strong inhomogeneous critical current density distribution in the TlBaCaCuO film is due to its granular structures and the existence of several structural phases. For c-axis oriented epitaxial YBaCuO thin film deposited in situ by laser ablation, the results indicate a less inhomogeneous critical current density distribution. The maximum local critical current density is less than 1.5 times the minimum local critical current density in the epitaxial thin film.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.351972

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3

Digitale Medien

Theoretical and experimental study of dissolution of inhomogeneities formed during spinodal decomposition in polymer mixtures (1992)

Akcasu, A. Ziya ; Bahar, I. ; Erman, B. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 97 (1992), S. 5782-5793

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: Dissolution (mixing or melting) of inhomogeneities formed during spinodal decomposition in binary polymer mixtures is studied both experimentally and theoretically. The details of the dissolution experiment with time-resolved light scattering on polystyrene/poly(vinylmethylether) are presented. The theoretical approach differs from that of Langer, Bar-on, and Miller in the way the fluctuations are treated in the nonlinear theory, and in the details of the calculations arising from the chain connectivity (polymer effect). The effect of mode coupling arising from nonlinearity on the relaxation rate is discussed. It is found both experimentally and theoretically that the wave number corresponding to peak intensity decreases in time asymptotically following a t−0.5 power law.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.463737

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4

Digitale Medien

X-ray photoelectron spectroscopy and Mössbauer study of Ho(Fe1−xMnx)2 compounds : The 6th joint magnetism and magnetic materials (MMM)−intermag conference (1994)

Tang, Y. J. ; Feng, Y. B. ; Luo, H. L. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 76 (1994), S. 6903-6905

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Cubic Laves compounds Ho(Fe1−xMnx)2 (x=0, 0.1, 0.2, 0.3) were investigated by XPS and Mössbauer measurements. It was found that the binding energy (BE) of compounds obtained by XPS remains almost the same for all the compounds and no chemical shift (δ) of the core-electron binding energy was found, which implies that no charge transfer takes place from Mn atoms to Fe atoms due to Mn substitution. Mössbauer study has shown that the average hyperfine fields and the deduced Fe moment decrease with increasing Mn content. It is considered that the variation of isomer shift (IS) due to Mn substitution obtained by Mössbauer measurement is mainly due to the size effect since the isomer shift (δ) for the compounds are almost linearly dependent on the volume; electron transfers seem to be of minor importance.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.358110

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5

Digitale Medien

Ga substitution effect on magnetic and magnetostrictive properties of TbFe2 compounds : The 6th joint magnetism and magnetic materials (MMM)−intermag conference (1994)

Tang, Y. J. ; Feng, Y. B. ; Luo, H. L. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 76 (1994), S. 7145-7147

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: In the present paper magnetic and magnetostrictive properties of Tb(Fe1−xGax)2 (x=0–0.2) compounds were investigated. It was found that the iron moment of the compounds does not seem to vary much for x≤0.12. The Curie temperatures of the compounds decrease continuously by substituting Ga for Fe, which was attributed to the decrease of the R-T coupling strength due to Ga substitution. The intersublattice coupling constant JRFe was evaluated by molecular field model. The decrease of JRFe with increasing Ga content was found and related to the decrease of the number of the Tb-Fe interaction pairs when replacing Fe with Ga. By using an x-ray diffractometer the samples were step scanned with Cu radiation at a higher Bragg angle 2θ ranging from 71° to 74° to study the cubic (440) reflection. The splitting of (440) reflection for X≤1.2 was clearly seen and the easy direction magnetostriction λ111 of the compounds was calculated. It was found that λ111 decreases with increasing Ga content. This was attributed to the decrease of magnetic properties of the compounds. The polycrystal magnetostriction λs of the compounds has also been studied.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.358016

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6

Digitale Medien

Physical and electrical investigation of ohmic contacts to AlGaAs/GaAs heterostructures (1994)

Taylor, R. P. ; Coleridge, P. T. ; Davies, M. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 76 (1994), S. 7966-7972

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The mechanism by which Ni-Au-Ge metallizations establish electrical contact to the two-dimensional electron gas (2DEG) in modulation-doped AlGaAs/GaAs heterostructures is investigated. Transmission electron microscopy was used to examine samples after electrical characterization by magnetoresistance measurements at cryogenic temperatures. We present a picture in which a 2DEG of reduced electron density exists under the deposited metallization. The success of the contacting procedure is described in terms of the magnitude of this density and the size, areal density, and penetration depth of a series of metallic spikes which establish the electrical link to the 2DEG. We suggest that the electrical behavior is not dominated by the current injection process at the spike/2DEG interface but is instead dictated by scattering from the array of antidots formed by the spikes and by a dependence of the 2DEG density on the size of the metallic pad. The implications of this picture for future nanostructure devices, featuring patterned ohmic metallization smaller than a micron, are discussed and preliminary results are reported. © 1994 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.357908

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7

Digitale Medien

Magnetic properties of nanometer-sized Fe4N compound (abstract) : The 6th joint magnetism and magnetic materials (MMM)-intermag conference (1994)

Feng, Y. B.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 76 (1994), S. 6594-6594

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Nanometer-sized magnetic materials have attracted a lot of attention because of their potential applications in the fields of ferrofluids, high density magnetic recording, and magnetic refrigeration. The sol-gel method has been considered to be effective for creating dispersions of small metal particles in nonmetallic materials. In this work, nanometer-sized Fe-N compound particles were prepared by nitrogenating the iron-boron oxide glass powders, which were synthesized by the sol-gel method from ethylene glycol gel. The magnetic properties of nanometer-sized iron nitride were measured by a vibrating sample magnetometer (VSM). The specific magnetic moment σ is equal to 132 emu/g and the coercivity Hc is 150 Oe. The phase composition was determined by using an x-ray diffractometer (XRD). The diffraction pattern shows that the sample consisted of a main phase of Fe4N and a small α-Fe phase. The crystallite size d of the Fe4N particles was estimated by Scherrer's formula, and is about 12 nm. The nanometer-sized Fe-N compound was also studied by using Mossbauer spectroscopy. The Mossbauer absorption pattern consisted of a ferromagnetic component superimposed on a superparamagnetic doublet. The ratio of superparamagnetic fraction to ferromagnetic is about 13%. It is shown that the sol-gel technique could be used to prepare ultrafine particles of Fe-N compound.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.358204

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8

Digitale Medien

Formation of crystallographic texture in rf sputter-deposited Cr thin films (1994)

Feng, Y. C. ; Laughlin, D. E. ; Lambeth, D. N.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 76 (1994), S. 7311-7316

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Although it is well known that Cr underlayers sputter deposited on glass or NiP/Al substrates have either the (002) or (110) textures, the mechanism of the formation of the crystallographic textures is not clear. A model is proposed for the formation of the crystallographic texture of sputter-deposited Cr thin films. A systematic set of experiments has been carried out to test the model. It was found that the (110) texture, which is usually found in Cr thin films deposited on substrates without preheating, can form at elevated temperatures (250 °C) when deposited at low Ar pressure or by applying substrate bias. The initial stage of the texture formation was also investigated by using very thin Cr films. It was found that the (002) texture can be initiated directly on the substrate surface, while the (110) texture appears not to form directly on substrate surface, but rather as a result of film growth. The proposed model is consistent with the experimental results. © 1994 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.358019

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9

Digitale Medien

Influence of size and magnetocrystalline anisotropy on spin canting anomaly in fine ferrimagnetic particles : The 6th joint magnetism and magnetic materials (MMM)-intermag conference (1994)

Han, D. H. ; Wang, J. P. ; Feng, Y. B. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 76 (1994), S. 6591-6593

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Fine equiaxed γ-CoxFe2−xO3 (x=0, 0.06) particles with a diameter ranging from 200 to 1000 A(ring) were prepared by chemical precipitation. The average crystallite sizes were determined from x-ray line broadening measurements. The saturation magnetization and magnetocrystalline anisotropy of the particles were determined by using the approach to saturation. An empirical linear dependence of the specific saturation magnetization σs on the specific surface area Sa of the fine crystallites was obtained in the form of σs(S)=σs(∞)(1−ASa). The slope A which reflects the surface spin canting anomaly is different for γ-Fe2O3 and γ-Co0.06Fe1.94O3 particles. Under the supposition of the fine crystallite consisting of two parts, i.e., the surface layer, whose magnetic moment cannot be turned entirely along the direction of the applied field, but makes an average canting angle with the field, and the inner part, whose magnetic moment can be aligned along the direction of the applied field, the above formula can be interpreted well. The different slope A for γ-Fe2O3 and γ-Co0.06Fe1.94O3 particles may be caused by the different anisotropies of the two series particles.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.358203

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10

Digitale Medien

Development of broad beam ion sources at CSSAR : Proceedings of fifth international conference on ion sources (1994)

Feng, Y. C. ; You, D. W. ; Kuang, Y. Z.

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 65 (1994), S. 1304-1306

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: High-energy and intense beam current broad beam ion sources have been developed for ion implantation and dynamic recoil mixing at CSSAR. The sources can be operated over beam energy and current ranges of 3–120 keV and 5–70 mA, respectively. For sputter coating of thin films, a series of focusing beam ion sources with different structures has also been developed. The energy and current range from 1–10 keV and 100–350 mA for different applications. For some applications, low-energy (below 100 eV) ion beams are required. CSSAR has developed a 6-cm-diam broad beam ion source. The source can be operated at beam energy 10–70 eV, and the beam current 15–80 mA has been extracted. Typical structures and operational data are given for the sources mentioned above. Recently a new type of broad beam metal ion source (Electron Beam Evaporation Metal Ion Source EBE) is being studied. Ion beams of several kinds of materials such as C, W, Ta, Mo, Cr, Ti, B, Cu, etc. have been extracted from the source. Typical operation conditions and ion yields are given in this paper.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1144987

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