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Last year, the KSTAR divertor material was changed from carbon to tungsten tiles. An optimized collection optic design for divertor Thomson scattering diagnostics in KSTAR was conducted for electron temperature (1–100 eV) and electron density (1 × 1018–1 × 1019 m−3) profile diagnostics. This diagnostic system will utilize a 1064 nm Nd:YAG laser directly from the K-top port toward the beam dump located at K-bottom, while collecting scattered light from five spatial points in the divertor area via collection optics situated in the j-middle port. Given spatial limitations, the solid angle of measurement points is limited, and the collection optic design facing the tungsten divertor is susceptible to stray light. So, the design of the collection optic is important for divertor Thomson scattering diagnostics. For optimal performance, we performed two types of collection optic designs: Cooke-triplet and double-Gaussian. We present performance ray tracing analysis results for both designs and derive the optimal design. [ABSTRACT FROM AUTHOR]

The below band-gap optical-absorption characteristics of GaxIn1-xSb alloy system have been reported. The different dependencies of the hole and electron absorption mechanisms on wavelength result in significant changes of the absorption characteristics with alloy composition. In the undoped Ga-rich alloy compositions that are p type in nature (due to residual holes resulting from native defects), the inter-valence-band absorption has been found to be the dominant absorption mechanism. With decreasing Ga (increasing indium) mole fraction, the hole to electron ratio decreases for undoped samples. For such samples, absorption due to electrons becomes significant. With n-type extrinsic doping, intervalley transitions are seen for certain Ga-rich compositions, which also alter the absorption characteristics. The dependencies of various absorption mechanisms as a function of wavelength have been analyzed and discussed in this paper. Based on the theoretical analysis presented in this paper, one can calculate the extrinsic doping level necessary for each alloy composition in order to obtain high optical transparency necessary for infrared optical applications. [ABSTRACT FROM AUTHOR]

The surface electronic structure of 1500-Å-thick Fe3O4(100) films has been investigated by spin-resolved photoemission spectroscopy with vacuum ultraviolet synchrotron radiation. The films, epitaxially grown on MgO(100) substrates using plasma-assisted molecular-beam deposition, are briefly exposed to air during transfer to the photoemission chamber. It is shown that clean surfaces of Fe3O4 films after exposure to air can be recovered through mild annealing in an oxygen atmosphere. The presence of the characteristic Verwey transition, as detected in the valence-band photoemission spectra, provides evidence for the excellent electronic quality at the surface of these films. The top of the valence band is found to be negatively spin polarized, with a value of ≈-50%; this result strongly points towards the localized nature of the 3d states in this system. [ABSTRACT FROM AUTHOR]

The resistive switching mechanism of 20- to 57-nm-thick TiO2 thin films grown by atomic-layer deposition was studied by current-voltage measurements and conductive atomic force microscopy. Electric pulse-induced resistance switching was repetitively (> a few hundred times) observed with a resistance ratio >102. Both the low- and high-resistance states showed linear log current versus log voltage graphs with a slope of 1 in the low-voltage region where switching did not occur. The thermal stability of both conduction states was also studied. Atomic force microscopy studies under atmosphere and high-vacuum conditions showed that resistance switching is closely related to the formation and elimination of conducting spots. The conducting spots of the low-resistance state have a few tens times higher conductivity than those of the high-resistance state and their density is also a few tens times higher which results in a ∼103 times larger overall conductivity. An interesting finding was that the area where the conducting spots do not exist shows a few times different resistance between the low- and high-resistance state films. It is believed that this resistance change is due to the difference in point defect density that was generated by the applied bias field. The point defects possibly align to form tiny conducting filaments in the high-resistance state and these tiny conducting filaments gather together to form stronger and more conducting filaments during the transition to the low-resistance state. [ABSTRACT FROM AUTHOR]

Neutron-transmutation-doped GaAs samples were prepared by irradiating the middle-level neutrons into the semi-insulating GaAs grown by a liquid encapsulated Czochralski method and subsequently implanted with Mn+. The characteristics of the Mn+-implanted neutron-transmutation-doped GaAs (namely, the implantation of Mn+ subsequent to neutron-transmutation-doping) were investigated by various measurements. The result of the energy dispersive x-ray peak displayed an injected Mn concentration of 9.65%. The photoluminescence peaks related to carbon and germanium acceptors were resolved, and the peaks related to Mn due to a neutral Mn acceptor were evidently observed. It is found that the proper activation for the neutral Mn acceptor starts from a relatively low annealing temperature of 600 °C for 15 min. The atomic force microscopy and magnetic forcemicroscopy images showed that magnetic clusters were well formed. The ferromagnetic hysteresis loop measured at 10 K was observed, and the temperature-dependent magnetization revealed that the two different phases exist at 135 and 360 K. The Curie temperature (Tc∼360 K) is caused by MnAs, which agrees with the clusters of the magnetic force microscopy image. [ABSTRACT FROM AUTHOR]

A method for determining the surface diffusion coefficient and the activation energy of Ge adatoms on Si(001) has been developed. Ge self-assembled quantum dots (SAQDs) grown on a relaxed SiGe buffer layer preferentially nucleate over a network of buried 60° dislocations. The surface sites over the buried dislocations act as sinks of Ge adatoms. When the average dislocation spacing becomes larger than the surface diffusion length of Ge adatoms, denuded zones free of Ge SAQDs appear on both sides of buried dislocations and separating the preferentially nucleated SAQDs from the randomly nucleated ones. The denuded zone width and the inter-dot spacing of randomly nucleated SAQDs are completely dependent on the surface diffusion coefficient. By varying the substrate temperature during the growth, the activation energy for the surface diffusion can be determined from the equilibrium inter-dot spacing of the randomly nucleated Ge SAQDs. Moreover, the pre-exponential term in the diffusion constant can be determined by using Fick’s first law and the observation that the total incident flux of Ge adatoms impinging on the denuded zones equals the average rate of volume increase of SAQDs over dislocations. The diffusion coefficient of Ge adatoms on Si (001) is found to be Ds≅2.53×10-7 exp(-0.676±0.03 eV/kT) cm2/s in the temperature range from 650 to 725 °C. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ga[sub 1-x]Mn[sub x]N epilayers with a well-ordered ferromagnetic structure were grown on sapphire (0001) substrates, using the plasma enhanced molecular-beam epitaxy technique. Ga[sub 1-x]Mn[sub x]N films were found to be homogeneous, and to exhibit n-type conductivity and ferromagnetic ordering with a Curie temperature (T[sub C]) above room temperature. This was confirmed by transmission electron microscopy, x-ray diffraction, and by magnetometry using a superconducting quantum interference device. The high-temperature (T=300 K) photoluminescence (PL) spectra exhibited Mn-related free-to-acceptor pair transitions for Ga[sub 1-x]Mn[sub x]N layers with x≈0.2% and x≈0.6%. A Mn acceptor level of a Ga[sub 1-x]Mn[sub x]N layer with low Mn content was found to be located around 330 meV above the top of the valence band, suggesting that Mn-bound holes in group-III nitrides exhibit effective-masslike behavior. The excitation and temperature-dependent PL provided convincing evidence of a band-edge exciton to acceptor transition. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Top synthetic spin valves with structure Ta/NiFe/CoFe/Cu/CoFe(P1)/Ru/CoFe(P2)/FeMn/Ta on Si (100) substrate with natural oxide were prepared by dc magnetron sputtering system. We have changed only the thickness of the free layer and the thickness difference (P1-P2) in the two ferromagnetic layers separated by Ru, and investigated the effect of magnetic film thickness on the interlayer coupling field in a spin valve with a synthetic antiferromagnet. As the free layer thickness decreased from 70 to 20 Å, the interlayer coupling field was increased due to the magnetostatic coupling (orange peel coupling). In the case of the thickness difference in the pinned layers, the interlayer coupling field agreed with the modified Néel model suggested in the top synthetic spin valve structures. However, in the case of t[sub P1]=t[sub P2], and t[sub P1]=t[sub P2]+5 Å, it was found that the interlayer coupling field could not be explained by the modified Néel ! model. The deviation of the modified Néel model at the dip zone could be due to the large canting of the pinned layers, which depend on applied field and different thickness in synthetic antiferromagnetic structure. The dependence of Cu thickness on the interlayer coupling field was investigated and 10 Oe of the interlayer coupling field was obtained when the Cu thickness is 32 Å. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the effects of silicon (Si)/(Si+carbon (C)) ratio in reaction gas stream on the growth and properties of monocrystalline Β-SiC films grown on Si (100) substrates via chemical vapor deposition. Method used to eliminate the subsurface damage caused by polishing; Dependence of growth rate and microstructure; Result of thermodynamic calculations.

Presents a study that analyzed the electrical properties and microstructure of indium arsenide ohmic contacts to n-type gallium arsenide semiconductors. Measurement of the contact resistance; Comparison of contacts prepared by sputter-deposition and evaporation; Effect of intervening oxide layer on indium arsenide and gallium arsenide interaction.

Presents a study that examined electrical properties and thermal stability of indium/tungsten ohmic contacts in gallium arsenide semiconductors. Analysis of the interfacial microstructure of the semiconductor; Measurement of the contact resistances; Influence of layer thickness on the contact resistances of the semiconductor.

Investigates the effects of dopants on surface-energy-driven secondary grain growth in silicon films. Description of the surface-energy-driven secondary grain growth; Theoretical background on the problem; Grain structure and grain-size distributions.

Presents a study that investigated the thermal stability of sulfur-treated indium phosphide (InP) by photoluminescence. Experimental details; Role of the surface states in InP in Schottky barrier formation and surface recombination velocity; Results of the study.

Focuses on a study which investigated the formation of amorphous layers and residual defects in SiF/BF[sub2] implanted and annealed silicon. Experimental details; Results and discussion; Conclusions.

Presents a study which investigated the magnetic properties of an Fe[sub73.5]Cu[sub1]Nb[sub3]Si[sub13.5]B[sub9] alloy with nanoscale crystalline structure as a function of the melt temperature. Background on the alloy; Experimental details; Results and discussion.

Presents a study which examined the structure and crystallization of low-pressure chemical vapor deposited silicon films with the use of silicon[sub2]hydrogen[sub6] gas. Experimental details; Results; Discussion.

Thermal stability of the present CoCrPt–SiO2 media becomes a more critical issue as recording density steadily increases. In the present study, thermal stability of the stacked media composed of high Ku CoPt–TiO2 and normal Ku CoCrPt–SiO2 was studied by changing stacking order and thickness of each layer while keeping a constant total thickness. When the CoPt–TiO2 layer was placed under the CoCrPt–SiO2 layer, negative nucleation field and coercivity increased much more than those of the reverse stacking case. Thermal stability of the CoPt–TiO2 bottom group was superior to that of the CoCrPt–SiO2 bottom group when measured by a spin stand. [ABSTRACT FROM AUTHOR]

Recent experiments have demonstrated high tunneling magnetoresistance (TMR) ratios in magnetic tunnel junctions (MTJs) with the MgO barrier. The CoFeB/MgO/CoFeB junctions showed better properties than the CoFe/MgO/CoFe junctions because the MgO layer had a good crystalline structure with (001) texture and smooth and sharp interface between CoFeB/MgO. In this work, the compositional changes in the MgO barrier and at the interface of CoFeB/MgO/CoFeB after the CoFeB crystallization were studied in annealed MTJs. X-ray photoelectron spectroscopy depth profiles were utilized for the as-deposited and 340 °C annealed specimens. Transmission electron microscope analyses showed that the MgO barrier had (100) texture on CoFeB in the junctions and CoFeB was crystallized in the annealed junctions. B in the bottom CoFeB layer diffused into the MgO barrier and B–oxide was formed at the interface of CoFeB/MgO/CoFeB after the CoFeB crystallization. The B behavior will be discussed. [ABSTRACT FROM AUTHOR]

We suggest a type of "goggle" cell shape and discuss its switching mechanism in comparison with conventional shapes such as rectangular and elliptical shapes. For the goggle shapes, the dependence of the switching characteristics on the saturation magnetization, the free layer thickness, and the aspect ratio was studied. We found that the "L"-like astroid curve with an enlarged writing margin could be obtained from a goggle shape, especially when the aspect ratio is smaller than 2. This seems to be closely related with the kink formation. We also found that the writing margin could be improved further as the saturation magnetization and thickness of the free layer was optimized. [ABSTRACT FROM AUTHOR]

p-type GaN epilayers were prepared by metalorganic chemical vapor deposition and subsequently implanted with Fe[sup +] ions. The properties of Fe[sup +] implanted GaN epilayers were investigated by various measurements. The results of photoluminescence measurement show that optical transitions related to Fe appear at 2.5 eV and around 3.1 eV. It was confirmed that the photoluminescence peak at 2.5 eV is a donor-Fe acceptor transition and the photoluminescence peak around 3.1 eV is a conduction band-Fe acceptor transition. Apparent ferromagnetic hysteresis loops measured at 10 and 300 K were observed, and the temperature-dependent magnetization displayed a ferromagnetic behavior persisting above 350 K. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In order to study the formation of polarization-induced two-dimensional electron gases (2DEGs), GaN/AlGaN/GaN heterostructures with different polarity were grown on sapphire (0001) substrates by plasma-assisted molecular-beam epitaxy. The polarity of GaN layers can be changed from the normal N-polarity to a Ga-polarity surface by inserting a thin Al metal layer prior to the growth of AlN buffer layer. The surface stability of each lattice polarity film was studied by in sim reflection high-energy electron diffraction. The polarity of the films and the location of 2DEGs in the heterostructure have been evaluated by investigating the carrier concentration profiles in the GaN/ AlGaN/GaN heterostructures. A simple model to explain the polarity change by a thin Al metal layer is proposed. [ABSTRACT FROM AUTHOR]

We report on the crystal structure of epitaxial (Ga,Mn)N films with Mn50.2% grown by plasma-enhanced molecular beam epitaxy, exhibiting n-type conductivity and room temperature ferromagnetism M[SUBs]0.76 emu/cm[SUP3], (H[SUBc]=90 Oe). The additional diffraction spots are found in the zone axis of B5@11 [1&1bar;00] for the (Ga,Mn)N epilayer due to a single twin orientation in the closed packed hexagonal matrix. High-order Laue zone measurements reveal the expansion of lattice parameter a (3.1851-3.1865 Å) by doping Mn, demonstrating that Mn ions substitute for Ga ions in the (Ga,Mn)N. [ABSTRACT FROM AUTHOR]

As-deposited Fe-Co-Ta-N soft magnetic thin films with a thickness of 250 nm were fabricated to achieve high saturation magnetization and excellent high-frequency characteristics. During sputtering, the input power was fixed at 450 W and the nitrogen partial pressure varied from 0% to 10%. In these films, the values of saturation magnetization and coercivity that were obtained were 17-23 kG and 3-6 Oe, respectively. The Fe[SUB78]Co[SUB8]Ta[SUB9]N[SUB5] (4% P[SUBN][SUB2]) film exhibits excellent high-frequency characteristics with an effective permeability of about 2000, which is maintained up to 700 MHz. Also, this film has B[SUBs]=21 kG, H[SUPc-hard]= 3 Oe, ρ=100 μΩ cm, and H[SUBk]=20 Oe. These high-frequency characteristics could result from the high values of the electrical resistivity and the magnetic anisotropy field. Furthermore, the corrosion resistance of these films was improved by the addition of nitrogen to give characteristics better than those of Co-Ni-Fe and Fe-Hf-N films. [ABSTRACT FROM AUTHOR]

GaMnN and Mg-codoped GaMnN films were grown in molecular beam epitaxy using a GaN single precursor. The structural, electrical, and magnetic properties were examined. The Mg-codoped GaMnN layers revealed room-temperature ferromagnetism. Codoping with Mg reduces the Mn incorporation, but increases the conductivity of the GaMnN films. At the same time, the saturation magnetization and coercivity have increased at room temperature. As this improvement was obtained with much reduced Mn concentration of ∼0.3%, the crucial role of the carriers for carrier-induced ferromagnetism in magnetic semiconductors is observed. [ABSTRACT FROM AUTHOR]

We investigated microstructural changes in a nano-oxide layer (NOL) with annealing in specular spin valves (SVs) by cross-sectional transmission electron microscopy and x-ray photoelectron spectroscopy analysis. In the SV annealed at high temperature of 400 °C, an increase in thickness and a local breakdown of the NOL were observed. This local coarsening of the NOL is closely related to the formation of Mn oxides in the oxide-rich part of the NOL through Mn diffusion. Thus, the chemical structure of the NOL changes to the structure with Mn oxide-rich content after annealing. [ABSTRACT FROM AUTHOR]

We present an efficient method for the formation of cobalt ferromagnetic quantum dots (FMQDs) by exposing a Nd: YAG laser (wavelength = 355 nm) on ferromagnetic thin films grown on Si substrates. Primary emphasis is placed on the simple and direct fabrication of the FMQDs without performing any micro- or nanopattering process. Scanned laser irradiation of low power causes localized segregation of ultrathin as-deposited films by the laser-induced heat, resulting in the fabrication of FMQDs. Observations by scanning electron microscope and atomic force microscope clearly confirm highly uniform controllable nanoscale FMQDs in our case. The average size and density of the FMQDs were about 10 nm and 2 × 10[SUP11]/cm[SUP2], respectively. Magnetic characteristics of the FMQDs were also measured by a superconducting quantum interference device at 5 K. [ABSTRACT FROM AUTHOR]

In this study, the magnetic properties and microstructures have been investigated in Co-Ni-Fe-N soft magnetic thin films with various film thicknesses (0.01-1.0 µm). As the film thickness decreases, the coercivity, electrical resistivity, and magnetic anisotropy field of these films increases from 1.1 to 7.90e, 53 to 188 µΩ cm, and 20 to 70 Oe, respectively. In addition, excellent high frequency characteristics were achieved in Co-Ni-Fe-N films with thicknesses less than 0.3 µm, where an effective permeability of, ∼ 1000 was maintained out to 700 MHz. Analysis results from XRD, TEM, and FMR show that a 0.1-µm-thick film is composed of an amorphous phase. This amorphous phase gradually changes to a crystalline phase with increasing film thickness. [ABSTRACT FROM AUTHOR]

We have investigated the effect of Co(Cr) substitution on magnetic properties of as-deposited Fe–Hf–N films. 4πMs increases with increasing Co content (3–16 at. %) and decreases with increasing Cr content. The film Fe[sub 56]Co[sub 16]Hf[sub 10]N[sub 18](at. %) shows excellent soft magnetic properties, with 4πM[sub s]∼16.8 kG, H[sub c]∼0.25 Oe, and effective permeability ∼4200 at 100 MHz. In Fe[sub 71]Cr[sub 3]Hf[sub 9]N[sub 17], the permeability is about 5200 at 100 MHz, while the values of 4πM[sub s] and H[sub c] are ∼14.6 kG and 0.5 Oe, respectively. In order to estimate the magnetic anisotropy, the angular dependency of the resonance magnetic field and linewidth were observed by ferromagnetic resonance (FMR) at 9.84 GHz. The Fe[sub 56]Co[sub 16]Hf[sub 10]N[sub 18] film shows a single resonance peak, whereas the as-deposited Fe–Hf–N films shows weak secondary peaks. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Induced anisotropy with a large energy of 6×10[sup 4] J/m[sup 3] is formed in an amorphous Sm–Fe based thin film by sputtering under an applied magnetic field of 500–600 Oe. The induced anisotropy results in a large anisotropy in magnetostriction, a strain anisotropy ratio reaching as high as 35, although intrinsic magnetostriction is affected only slightly. The large strain anisotropy allows one to realize a large strain in a particular direction and, hence, it is of significant practical importance. Induced anisotropy is also found to be formed by postannealing under applied magnetic field, but the magnitude of anisotropy energy formed is very small. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The magnetic and structural properties of as-sputtered nanocrystalline Fe–Al–O films, fabricated by a magnetron sputtering apparatus, are investigated as a function of the sputtering input power and the contents of Al and oxygen. A nanocrystalline Fe[sub 88.5]Al[sub 3.5]O[sub 8.0] film is found to have 4πM[sub s] of 18.2 kG, H[sub c] of 0.6 Oe, μ[sub eff] of 4600 up to 100 MHz. These excellent soft magnetic properties and high frequency characteristics result from nanocrystalline structure, high electrical resistivity, and moderate anisotropy field. These values are sufficient to apply to a high-density recording head. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study that fabricated Fe-Hf-C-N films with soft magnetic properties. Experimental procedures; Results; Discussion.

Presents a study which investigated the effects of aluminum on the soft magnetic properties of nanocrystalline iron[sub73.5-x]aluminum[subx]copper[sub1]niobium[sub3]silicon[sub13.5]boron[sub9] alloy ribbons. Experimental details; Results and discussion; Conclusions.

Discusses a study that investigated the metalloid effect on magnetic properties and microstructures of iron-based alloy with ultrafine grain structures. Magnetic softness of iron based Fe-Cu-Nb-Si-B alloys with ultrafine grains prepared by crystallization from amorphous states; Phases and microstructures of the annealed samples used; Temperature dependence of the residual magnetization.

Studies the effect of copper and niobium addition on the crystallization processes and soft magnetic properties for iron-silicon-boron alloys. Experimental procedures; Information on the permeability values of alloys; Thermograms of the amorphous alloys.

In fluorescence spectroscopy and imaging, fluorescence lifetime measurement—assessing the average time fluorophores spend in their excited state before returning to their ground state—offers a number of advantages over quantifying fluorescence intensities that include resistance to photobleaching and independence from fluorophore concentration, excitation intensity, and measurement methodology. Despite growing interest, fluorescence lifetime techniques frequently mandate relatively complex instrumentation, slow data acquisition rates, and significant data analyses. In this work, we demonstrate the feasibility of measuring fluorescence lifetimes using off-the-shelf analog silicon photomultipliers and switched-capacitor array waveform sampling techniques, with precision matching that of much larger and more elaborate commercial instruments. [ABSTRACT FROM AUTHOR]

Luminescence in the near band-edge spectral region of Mg-doped GaN films grown by metalorganic chemical vapor deposition has been studied at liquid-helium temperatures. Radiative transitions at 3.37 and 3.416 eV were observed to evolve in cathodoluminescence spectra during electron-beam irradiation at 5 kV. The intensity of the 3.37 eV peak correlates monotonically with the resistivity of the films. By annealing the films in N2 and N2/H2 atmospheres, the 3.37 and 3.416 eV transitions are shown to be related to hydrogen. [ABSTRACT FROM AUTHOR]