bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-organization of GeAs nanodots in relaxed Si0.5Ge0.5 alloys
Authors: Gaiduk P. I. , Nylandsted Larsen A. , Lundsgaard Hansen J.
Published: July 2002

We report on the bimodal distribution and long-range ordering of GeAs nanodots obtained in strain-relaxed epitaxial Si0.5Ge0.5 alloy layers after arsenic implantation and rapid thermal annealing. GeAs dots of two different average sizes around 15 and 55 nm are found after high temperature rapid thermal annealing. The larger dots are of elliptical shape and located at the surface region; they are distributed preferably along 〈110〉 directions which correlates well with the observed cross-hatch pattern. The origin of the bimodal precipitate distribution as well as of the long-range ordering effect of the GeAs nanodots is discussed in terms of strain-induced nucleation and diffusion-limited growth.
Phonon modes of GaNyP1−y (0.006⩽y⩽0.0285) measured by midinfrared spectroscopic ellipsometry
Authors: Leibiger G. , Gottschalch V. , Kasic A. , Schubert M.
Published: July 2002

Midinfrared spectroscopic ellipsometry reveals the two-phonon mode behavior of GaNyP1−y for nitrogen compositions 0.006⩽y⩽0.0285. The single layers (∼350 nm) studied were grown by metalorganic vapor-phase epitaxy on GaP substrates with orientations (001), and (001) with 5° off toward [110]. Line-shape analysis of the midinfrared response allows determination of the transverse- and longitudinal-optical phonon frequencies of the GaP- and GaN-like phonon modes. The polar strength of the GaN lattice resonance increases linearly with y, which can be used to monitor the nitrogen content of GaNyP1−y.
Epitaxial growth and properties of ferromagnetic co-doped TiO2 anatase
Authors: Chambers S. A. , Thevuthasan S. , Farrow R. F. C. , Marks R. F. , Thiele J. U. , Folks L. , Samant M. G. , Kellock A. J. , Ruzycki N. , Ederer D. L. , Diebold U.
Published: July 2002

We have used oxygen-plasma-assisted molecular-beam epitaxy (OPA-MBE) to grow CoxTi1−xO2 anatase on SrTiO3(001) for x=∼0.01–0.10, and have measured the structural, compositional, and magnetic properties of the resulting films. Whether epitaxial or polycrystalline, these CoxTi1−xO2 films are ferromagnetic semiconductors at and above room temperature. However, the magnetic and structural properties depend critically on the Co distribution, which varies widely with growth conditions. Co is substitutional in the anatase lattice and in the +2 formal oxidation state in ferromagnetic CoxTi1−xO2. The magnetic properties of OPA-MBE grown material are significantly better than those of analogous pulsed laser deposition-grown material.
Negligible oxygen liberation during bipolar electric cycling of ferroelectric lead zirconate titanate ceramics
Authors: Nuffer Jürgen , Lupascu Doru C. , Rödel Jürgen , Schroeder Michael
Published: July 2002

The long-standing question whether or not oxygen gas is liberated from the perovskite lattice during fatigue of ferroelectric lead zirconate titanate ceramics is addressed. During cycling, the surrounding gas atmosphere of the sample was analyzed continuously by a mass spectrometer. It was found that, in contrast to previous statements in the literature, the oxygen detected originates from air dissolved in the surrounding liquid. An upper limit for oxygen liberation from the sample is given. We conclude that all mechanistical approaches for ferroelectric fatigue based on oxygen liberation are in need of revision.
Micromagnetic disorder in antiparallel biased spin valves
Authors: Marrows C. H. , Creeth G. L. , Stanley F. E. , Hickey B. J. , Aitchison P. R. , Crawford M. , Chapman J. N.
Published: July 2002

The reorientation of antiferromagnetically coupled Co layers comprising the pinned layers of an antiparallel biased spin valve is reported. Initially, the lower Co layer is saturated in the growth field in the deposition chamber, but it reorients as the upper Co layer grows to be thicker than the lower one. We have investigated the nature of this reorientation by ex situ transport measurements and Lorentz microscopy, and found it highly inhomogeneous, leading to a complex in-plane domain pattern. This results in a reduction of the giant magnetoresistance of the spin valves close to the balance point, where the benefits of the antiparallel biasing are greatest.
Oxidation kinetics of tunnel barrier and its effect on exchange bias of proximity interface
Authors: Bae Seung-Young , Shin Kyung-Ho , Lee Je-Hyung , Rhie Keung-Won , Lee Kyoung-Il , Ha Jae-Geun , Wang Shan Xiang
Published: July 2002

Atomic migration in metallic multilayers of magnetic tunnel junction (MTJ), and consequent compositional modulation at the interface during plasma oxidation of an Al tunnel barrier is reported. Surprising effects of such modulation in our specific MTJ appear as the systematic increase in exchange bias of the NiFe buffer layer beneath an FeMn antiferromagnet. Cation-current-limited oxidation of the Al metal layer drives atomic migration in the underlying multilayers to compensate for the cation vacancies created in the metal side of the metal/oxide interface. The condition of oxide growth which manifests different migration behavior is also discussed.
Visualization of intracellular Ca2+ dynamics with simultaneous two-photon-excited fluorescence and third-harmonic generation microscopes
Authors: Barille R. , Canioni L. , Rivet S. , Sarger L. , Vacher P. , Ducret T.
Published: July 2002

We present a promising development of third-harmonic generation (THG) coupled with two-photon excited fluorescence (TPEF) in laser scanning microscopy to study in vivo glial human cells. In this letter, intracellular Ca2+ dynamics in biological cells are shown. The THG microscopy allows visualizing precisely the localization of the Ca2+ release whereas TPEF microscopy only gives functional mechanisms.
Evaluation of the precipitate contribution to the infrared absorption in interstitial oxygen measurements in silicon
Authors: Sassella A. , Borghesi A. , Pivac B. , Porrini M.
Published: July 2002

The spurious contribution of oxide precipitates to the infrared absorption of interstitial oxygen in silicon is determined from spectra collected at 7 K for samples with different initial interstitial oxygen Oi concentration subjected to a three-step thermal treatment. These data can be used to correct the residual Oi values determined at room temperature following the standard procedure from the intensity of the 1107 cm−1 absorption band. The error in residual Oi is found to reach values on the order of 2×1017 atoms/cm3 for samples with initial Oi content higher than 6.5×1017 atoms/cm3.
Nonlinear effects in YBa2Cu3O7−x microstrip resonators on sapphire
Authors: Zaitsev A. G. , Schneider R. , Linker G. , Ratzel F. , Smithey R. , Geerk J.
Published: July 2002

Power-induced nonlinear effects, i.e., the reduction of the quality factor, the distortion of the resonance peaks, and the two-tone intermodulation distortion (IMD), were experimentally examined by using 2.3 GHz microstrip resonators prepared from double-sided YBa2Cu3O7−x (YBCO) films on CeO2-buffered sapphire. The resonators exhibited advanced performance with an unloaded quality factor of 80 000 at 63 K up to a circulating power Pcirc of 0.5 W and an IMD third-order interception point estimated at Pcirc≈400 W. We found that the nonlinear effects in these resonators were produced by the power-dependent surface resistance Rs of the YBCO films, whereas the variation of the surface reactance was negligible. Both the presence of the high-order IMD products and the dependence of their amplitude on the microwave power, indicate a Rs(H)∝cosh H relationship, where H is the amplitude of the microwave magnetic field at the film surface. Such a dependence agrees with the direct measurements of the power handling capability.
Wet plasma reactor for remidiation of SO2
Authors: Seethamsetty S. , Dhali S. K. , Dave Bakul
Published: July 2002

In pollution control applications, the presence of water in the electrical discharge enhances oxidation of pollutants. The results of an electrical discharge in gas when it flows through a heterogeneous mixture of water and dielectric pellets are reported. The discharge in the wet plasma reactor is more uniform compared to dry dielectric-barrier reactors. The electrical characteristics of such a discharge are discussed. Also the results of removal of SO2 with the wet reactor are reported. The wet reactor was found to be 5–10 times more energy efficient in removing SO2 compared to conventional dry plasma reactors.
Magnetotunneling spectroscopy of resonant anticrossing in terahertz intersubband emitters
Authors: Williams Benjamin S. , Callebaut Hans , Hu Qing , Reno John L.
Published: July 2002

Intersubband transport and electroluminescence has been investigated in a double-quantum-well structure based on an intrawell (vertical) THz radiative transition. Magnetotunneling spectroscopy was used to determine subband energies, including the minimum energy separation (∼1.7 meV) between two anticrossed levels. The presence of this anticrossing indicates that in this structure, electron removal from the lower radiative state should be modeled by coherent resonant tunneling rather than incoherent sequential tunneling.
Does beryllium doping suppress the formation of Ga vacancies in nonstoichiometric GaAs layers grown at low temperatures?
Authors: Gebauer J. , Zhao R. , Specht P. , Weber E. R. , Börner F. , Redmann F. , Krause-Rehberg R.
Published: July 2002

We investigate native defects in nonstoichiometric GaAs layers grown at low temperatures by molecular-beam epitaxy (LT-GaAs) doped with Be. Ga vacancies (VGa) are found by positron annihilation in all layers. The concentration of VGa is independent of the Be doping in contrast to the previous belief that it decreases. Simultaneously, the concentration of As antisite defects (AsGa) was measured by optical absorption. We find the same relationship between VGa and AsGa concentrations as reported earlier for undoped LT-GaAs. Thus, Be doping has no significant influence on the incorporation of native point defects in LT-GaAs. The thermal stability of such material must therefore be explained otherwise.
Ab initio study of quantum confined unpassivated ultrathin Si films
Authors: Agrawal B. K. , Agrawal S.
Published: July 2002

An ab initio study of the electronic structure of the one-dimensional quantum-confined crystalline ultrathin Si (100) films both with the unreconstructed p(1×1) and the reconstructed c(2×2) film surfaces in a large thickness range of 2.7–29.7 Å has been made after employing a self-consistent full potential linear muffin tin orbital method along with the density functional theory in local approximation. A relatively large unit cell of 28 layers has been employed. In the case of the unreconstructed p(1×1) surface, the dangling bond states fill the fundamental energy gap completely and these states are weakly localized, i.e., the wave functions of these states die out in the inner region of the film slowly. After the c(2×2) surface reconstruction, the bonding and the antibonding dangling bond states are seen to lie near the valence band maximum and the conduction band minimum in the fundamental energy gap, respectively, and are again weakly localized. There remain dangling bond states within the gap after reconstruction. The separation between the two surface Si atoms in a dimer shows quite an appreciable change of about 36–40%. The band gaps of the various films remain practically unchanged after surface reconstruction; the changes lie well within 6%. The present results give convincing theoretical evidence for the occurrence of the weakly localized dangling bond states and the absence of too much localized states in quantum-confined systems, which may be responsible for the occurrence of luminescence observed in a comparatively low energy region in the quantum-confined nanostructures, e.g., in the infrared region in porous silicon. The presently predicted exponential rise of the band gap with the decrease in the quantum-confined size in the ultrathin film region is in sharp contrast to an approximate linear rise in the band gap observed in the spectroellipsometric measurements.
Magnetic anisotropy in prismatic nickel nanowires
Authors: Sun L. , Searson P. C. , Chien C. L.
Published: July 2002

Nickel nanowire arrays with a diamond-shaped cross section and the same orientation have been fabricated in nanoporous single mica crystal membranes by electrodeposition. All wires are 5 μm long with an effective diameter of 120 nm. The sample can be considered as a collection of laterally and vertically aligned identical micromagnetic prisms. We report on the magnetic anisotropy due to the quasi-one-dimensional wire shape and diamond cross section.
Radiation sensitivity reduction in deuterium annealed Si–SiO2 structures
Authors: Chavez J. R. , Devine R. A. B. , Shedd W. M.
Published: July 2002

The x-ray radiation sensitivity of Si–SiO2–Si structures annealed at 420 °C in hydrogen containing forming gas and deuterium containing forming gas is compared. Irradiations carried out without electrical bias and with ±0.5 MV cm−1 up to doses ∼2M rad (SiO2) consistently indicate that positive fixed oxide charge is generated ∼1.5 times more efficiently in hydrogen-annealed oxides as compared to deuterium-annealed oxides. This result suggests that some radiation-induced positive charge creation involves defects passivated with hydrogen/deuterium during the forming gas anneal sequence.
Photoemission spectroscopy study of Alq3 and metal mixed interfaces
Authors: Kwon Soonnam , Kim Shin Cheul , Kim Youngkyoo , Lee Jae-Gyoung , Kim Sunwook , Jeong Kwangho
Published: July 2002

The electronic structures of mixed layers of tris (8-hydroxy-quinoline) aluminum (Alq3) and metal (Au and Al) were studied by ultraviolet and x-ray photoelectron spectroscopy (UPS and XPS). The devices with a mixed layer between Alq3 and the cathode were fabricated. The barrier height for electron injection was reduced by doping metals (Au or Al) into Alq3. The doping enhanced the performance of the device. From the XPS study, the doped Au metal did not react with Alq3 and in addition, the doped Al metal reacted slightly with Alq3. From the UPS study, the highest occupied molecular orbit shifted to a higher binding energy for both metal mixed layers. From these studies, it is concluded that the enhanced device characteristics come from the barrier height reduction by the metal doped in Alq3 rather than from the charge transfer complex induced by the reaction of Alq3 and metal.
Ordered growth of nanocrystals via a morphological instability
Authors: Eggleston J. J. , Voorhees P. W.
Published: July 2002

Nanocrystal formation on patterned substrates during heteroepitaxy is studied. Deposition on a substrate with a mesa induces a qualitatively new morphological instability that is driven solely by capillarity. If the film possesses a lattice parameter misfit with the substrate, this instability then propagates as a traveling wave along the substrate. This traveling wave yields large regions of highly ordered nanocrystals. Strongly anisotropic surface energy greatly increases the growth rate of the instability of a planar film and, thus, decreases the distance over which the traveling wave propagates. Even in this case, however, deposition on a substrate with a periodic arrangement of mesas can yield highly ordered arrays of nanocrystals.
Multilayer TiC/TiN diffusion barrier films for copper
Authors: Yoganand S. N. , Raghuveer M. S. , Jagannadham K. , Wu L. , Karoui A. , Rozgonyi G.
Published: July 2002

TiC/TiN thin films deposited by reactive magnetron sputtering on Si (100) substrates were investigated by transmission electron microscopy for microstructure and by deep level transient spectroscopy (DLTS) for diffusion barrier against copper. TiN thin films deposited on Si substrates at a substrate temperature of 600 °C were textured, and TiC thin films deposited at the same temperature were polycrystalline. TiC/TiN multilayer films also showed the same characteristics with the formation of an additional interaction layer. The diffusion barrier characteristics of the TiC/TiN/Si were determined by DLTS and the results showed that the films completely prevented diffusion of copper into Si.
Real time resistivity measurements during sputter deposition of ultrathin copper films
Authors: Barnat E. V. , Nagakura D. , Wang P.-I. , Lu T.-M.
Published: July 2002

Measurements of the electrical resistivity of thin copper films sputtered onto silicon dioxide, in real time, are reported. The electrical resistivity is shown to strongly depend on the film’s thickness for thicknesses below the bulk mean free path of copper (39 nm). Model fits to the electrical resistivity combined with ex situ atomic force microscopy and transmission electron microscopy suggest that the average grain size plays a dominant role in the resistivity during growth. Furthermore, observations are made on the relaxation of the electrical resistivity after the growth (by sputtering) is terminated, at room temperature. Both the magnitude and the time scale of change in the electrical resistivity are observed to be a function of the film’s thickness.
Orientation effects in tBN/cBN interfaces: A transmission electron microscopic study
Authors: Li Quan , Bello I. , Marks L. D. , Lifshitz Y. , Lee S. T.
Published: July 2002

The orientation between cubic boron nitride (cBN) crystallites and the tBN layers on which they grow was studied using high-resolution transmission electron microscopy. BN films were prepared by radio-frequency magnetron sputtering under conditions leading to the formation of ∼100% cBN films grown on a preceding tBN layer. Two types of orientations were observed: (i) cBN layers grown on the edges of the tBN(0002) planes so that the cBN{111} planes are parallel to the tBN(0002) planes (as reported previously by many authors), (ii) cBN layers grown on curved tBN(0002) planes with no orientation to the tBN planes. The first type of cBN growth is associated with stress leading to delamination of cBN films thicker than 100 nm. The second type is associated with reduced stress enabling the growth of much thicker (∼500 nm) films at a relatively low (450 °C) substrate deposition temperature. These results may be helpful in the fabrication of thick cBN films and improving our understanding of the cBN nucleation process.
Anharmonicity of the C–H stretch mode in SiC: Unambiguous identification of hydrogen–silicon vacancy defect
Authors: Gali A. , Aradi B. , Heringer D. , Choyke W. J. , Devaty R. P. , Bai S.
Published: July 2002

Using first principles calculations, the vibronic properties of hydrogen in a silicon vacancy (VSi+H) are investigated in 3C–SiC. The calculations show that the neutral VSi+H complex, which can bind an exciton, is stable only in lightly p-type SiC. This result is consistent with the experimental findings. The calculations are able to account well for the observed anharmonicity of the C–H stretch vibrations, up to the third harmonic, and for the isotope effects.
InGaN self-assembled quantum dots grown by metalorganic chemical-vapor deposition with indium as the antisurfactant
Authors: Zhang J. , Hao M. , Li P. , Chua S. J.
Published: July 2002

Nanometer-scale InGaN self-assembled quantum dots have been formed in an InGaN single-quantum-well structure on a (0001) sapphire substrate with In as the antisurfactant using low-pressure metalorganic chemical-vapor deposition. High-resolution transmission electron microscopy reveals that the average dimensions of InGaN nanometer-scale structures are as small as 4 nm wide and 1.5 nm high. Strong photoluminescence emission of the InGaN quantum dots was observed at room temperature with an emission peak of about 2.56 eV (485 nm) and a full width at half maximum of about 150 meV (30 nm). The choice of In as the antisurfactant also avoids the incorporation of foreign atoms in the active layers.
Large second harmonic response in ZnO thin films
Authors: Wang Gang , Kiehne G. T. , Wong G. K. L. , Ketterson J. B. , Liu X. , Chang R. P. H.
Published: July 2002

The second-order susceptibilities in the ZnO films have been studied systemically. In very thin films, we observe an enhancement of second-order susceptibilities, which is larger than that of single-crystal ZnO. It was also observed that the second-order susceptibilities for ZnO films depend on the thickness but not on the film growth technique used (reactive sputtering or plasma-enhanced chemical vapor deposition). We suggest a mechanism to explain the reduction in the second-order susceptibilities of the thicker films.
Improved copper detection in hydrofluoric acid by recombination lifetime measurements on dedicated silicon substrates
Authors: Boehringer Matthias , Hauber Johann
Published: July 2002

Copper (Cu) adsorption from diluted hydrofluoric acid (DHF) onto bare silicon surfaces strongly depends on the substrate doping. On highly phosphorus-doped silicon, the adsorption rate is up to three orders of magnitude larger than on moderately doped silicon. This may open a gap between Cu-induced semiconductor device degradation and the detection of Cu contaminations in DHF by minority carrier lifetime measurements. Using dedicated copper monitor wafers where a highly phosphorus-doped backsurface ensures strong Cu adsorption while a moderately doped frontsurface enables minority carrier lifetime measurements, we are able to improve the limit of detection for Cu in DHF by two orders of magnitude.
Microstructure-size dependence of the 1.520 μm Er3+ luminescence lifetime in Al2O3–ZrO2 eutectic melt growth composites
Authors: Merino R. I. , Pardo J. A. , Peña J. I. , Orera V. M.
Published: July 2002

The radiative lifetime of the I13/24 level of Er3+ was modified up to 15% by changing the microstructure in laser-floating-zone-grown Er3+-doped Al2O3–ZrO2 eutectic melt growth composites. Erbium enters only the higher-refractive-index ZrO2 phase, which occupies 30% of the volume of the sample. The lifetimes of S3/24 (545 nm) and I13/24 (1520 nm) Er3+ levels were measured at 10 K and room temperature in different microstructures. The variation in the lifetime of this last level with interphase spacing is due to the change of the available electromagnetic modes at 1520 nm due to the change in the optical environment of the luminescent ion.
Electrical properties of strained AlN/GaN superlattices on GaN grown by metalorganic vapor phase epitaxy
Authors: Yamaguchi Shigeo , Iwamura Yasuo , Watanabe Yasuhiro , Kosaki Masayoshi , Yukawa Yohei , Nitta Shugo , Kamiyama Satoshi , Amano Hiroshi , Akasaki Isamu
Published: July 2002

We have studied the temperature dependence of electrical properties of crack-free strained AlN/GaN superlattices (SLs) on GaN grown by metalorganic vapor phase epitaxy. A (0001) sapphire substrate was used. A single AlN on GaN and one and five pairs of AlN/GaN superlattices were grown using N2 carrier gas. The thicknesses of AlN and GaN in the superlattices were 1 and 5 nm, respectively. Hall measurements were performed at 295–20 K. The five pairs of AlN/GaN SLs on GaN showed an electron mobility of 9925 cm2/V s and a sheet carrier density of 1.14×1012 cm−2 at 20 K, and 1354 cm2/V s and 1.14×1012 cm−2 at 295 K.
Effect of LiF/metal electrodes on the performance of plastic solar cells
Authors: Brabec Christoph J. , Shaheen Sean E. , Winder Christoph , Sariciftci N. Serdar , Denk Patrick
Published: July 2002

The insertion of thin interlayers of LiF under the negative metal electrode (Al and Au) of bulk heterojunction solar cells significantly enhances the fill factor and stabilizes high open circuit voltages. Compared to devices without the LiF interfacial layer, the white light efficiencies increase by over 20% up to ηeff∼3.3%. Substitution of the LiF by another insulating interlayer SiOx results in lower overall efficiencies. In the case of a LiF/Au electrode, substantial efficiency enhancement is observed compared to a pristine Au electrode and white light efficiencies up to ηeff∼2.3% are reported.
Stable bit formation in polyimide Langmuir–Blodgett film using an atomic force microscope
Authors: Yano K. , Ikeda T.
Published: July 2002

Nanometer scale recording bits were stably fabricated in polyimide (PI) Langmuir–Blodgett (LB) films on atomically flat Au (111) surfaces using an atomic force microscope (AFM). The bits are written by voltage application through the AFM probe only until the conductance increases. This method eliminates the influence of the variation in the transition time and therefore the degradation of the tip of the probe. 1 Mbit stable writing can be realized. The overall error rate is less than 2×10−3. The results show that an AFM based memory system with PI LB films is a hopeful candidate to realize a scanning probe microscope based memory system.
X-ray-induced phase transformation in congruent and vapor-transport-equilibrated lithium tantalate and lithium niobate
Authors: Shur V. Ya. , Blankova E. B. , Rumyantsev E. L. , Nikolaeva E. V. , Shishkin E. I. , Barannikov A. V. , Route R. K. , Fejer M. M. , Byer R. L.
Published: July 2002

We have discovered an effect of a partially reversible x-ray-induced increase of diffuse x-ray scattering in both congruent and vapor-transport equilibrated single-crystalline lithium niobate and lithium tantalate. The effect has been attributed to x-ray-induced decay of the ferroelectric phase at room temperature. The x-ray-induced change of the switching current and hysteresis loops observed is in accord with this assumption.
Spatially resolved electron temperature measurements with a microfabricated retarding field analyzer
Authors: Sowa M. J. , Blain M. G. , Jarecki R. L. , Stevens J. E.
Published: July 2002

Electron temperature (Te) is an important parameter to quantify in the high-density plasmas commonly used in semiconductor manufacturing. Te is characteristic of the electron energy distribution which determines the plasma density and distribution of neutral and ionic species. Through application of theoretical considerations for the presheath and sheath, Te can be estimated from the ion energy distribution to a floating substrate. Utilizing microfabricated retarding field analyzers (RFAs) to measure the local ion energy distribution to a floating surface, spatially resolved Te measurements in an inductively coupled argon plasma have been made. Quantitative agreement between the RFA and Langmuir probe Te measurements was observed and the RFA Te measurements display the expected power, pressure, and spatial dependencies.
Photoconductivity in confined gallium
Authors: Fedotov V. A. , Woodford M. , Jean I. , Zheludev N. I.
Published: July 2002

We report on the observation of photoconductivity in elemental gallium confined at an interface with glass. The effect is associated with a fully reversible light-induced structural transformation in the metal, which affects a surface layer only a few nanometers thick. The effect has the potential for applications in optically fast, broadband photodetectors.
Templated electrodeposition of patterned soft magnetic films
Authors: Azzaroni O. , Schilardi P. L. , Salvarezza R. C.
Published: July 2002

Fabrication of patterned magnetic CoNiFe films by the thiol-assisted templated electrodeposition method is described. This method involves electrodeposition of the alloy components from their ionic species in solution on a dodecanethiol-covered Cu template. The ultrathin alkanethiol layer enables nano/micrometer pattern transfer and easy detachment of the magnetic film from the template. This method opens the possibility of fabricating nano/micropatterned chemically complex alloy structures in an extremely easy way with very few intermediate steps.
Quantitative measurement of Cr segregation in Co0.8−xCrxPt0.1B0.1 recording media by scatter diagram analysis
Authors: Grogger Werner , Krishnan Kannan M. , Ristau Roger A. , Thomson Thomas , Harkness Samuel D. , Ranjan Rajiv
Published: July 2002

We describe the scatter diagram analysis of chemically resolved energy-filtered transmission electron microscopy (EFTEM) images and demonstrate its application in obtaining quantitative information about the segregation of Cr on the nanometer scale. The recording performance of Co–Cr based magnetic media depends critically on the microstructure of the thin film alloy, i.e., the degree of segregation of Cr to the grain boundaries determines the extent of magnetic isolation that can be achieved. Magnetic isolation of the grains reduces transition widths and thereby allows increased recording densities. The EFTEM results obtained correlate well with both the magnetic properties and recording performance of the media; i.e., a higher Cr content of 16 at. % (compared with a 10 at. % sample) shows substantial segregation of Cr with about 8% (0.06%) of the image area, most of it at the grain boundaries, having a Cr concentration which is higher than 24 at. %, and a medium signal to noise ratio of 17.8 dB (15.3 dB).
Optical confinement in CdTe-based photonic dots
Authors: Obert M. , Wild B. , Bacher G. , Forchel A. , André R. , Dang Le Si
Published: July 2002

We demonstrate three-dimensional optical confinement in CdTe-based microcavities. While the vertical confinement is determined by epitaxially grown CdMnTe/CdMgTe Bragg mirrors, the lateral confinement is achieved by defining pillar structures with electron beam lithography and reactive ion etching. The optical confinement is shown by a size-dependent energy splitting between the fundamental and higher photonic modes.
Band discontinuity in the GaAs/AlAs interface studied by in situ photoemission spectroscopy
Authors: Okabayashi J. , Ono K. , Mano T. , Mizuguchi M. , Horiba K. , Nakamura K. , Fujimori A. , Oshima M.
Published: July 2002

In order to investigate the valence-band discontinuity of the GaAs/AlAs interface, the thickness dependence of the photoemission spectra of a GaAs layer in situ deposited on AlAs by molecular-beam epitaxy has been studied. Although the interface is atomically abrupt, the electronic structure in the interface region displays Al1−xGaxAs alloy-like behaviors. The valence-band maximum as well as the Ga 3dcore level show a gradual shift as a function of GaAs layer thickness of less than 2 nm (8 monolayers), which indicates that interface formation needs about 2 nm thickness for the electronic structure of the GaAs layer to become that of bulk GaAs.
Misfit defect formation in thick GaN layers grown on sapphire by hydride vapor phase epitaxy
Authors: Valcheva E. , Paskova T. , Persson P. O. Å. , Hultman L. , Monemar B.
Published: July 2002

The nucleation and microstructure of large-scale columnar domains present in hydride vapor phase epitaxial (HPVE)-GaN layers grown directly on sapphire have been studied using cathodoluminescence and transmission electron microscopy. The domains are distributed in a quasicontinuous layer close to the GaN/sapphire interface. The domain boundaries are found to be associated with stacking mismatch defects. They are initiated at steps on the sapphire surface and are formed between nucleation islands growing on adjacent terraces. The formation of these domains in the initial stages of HVPE-GaN heteroepitaxial growth is proposed to play an important role in the strain relaxation mechanism.
Experimental studies of two-dimensional coaxial Bragg structures for a high-power free-electron maser
Authors: Cross A. W. , Konoplev I. V. , Ronald K. , Phelps A. D. R. , He W. , Whyte C. G. , Ginzburg N. S. , Peskov N. Yu. , Sergeev A. S.
Published: July 2002

The experimental studies of two-dimensional (2D) coaxial Bragg structures are presented. These structures, which realize 2D distributed feedback, have been recently proposed as a method of producing gigawatt power level spatially coherent radiation from a free-electron maser driven by a large-size relativistic electron beam of annular geometry. The experimentally obtained frequency dependence of transmission coefficients for the 2D Bragg structures are in good agreement with theoretical predictions that demonstrates the operation of the two-dimensional Bragg scattering mechanism.
Dispersion, refinement, and manipulation of single silicon nanowires
Authors: He J. Z. , Xu J. B. , Xu M. S. , Xie Z. , Wilson I. H. , Ma X. L. , Li Q. , Wang N. , Hung L. S. , Lee C. S. , Lee S. T.
Published: July 2002

We have successfully dispersed silicon nanowires in liquid by a mild etching treatment. A transmission electron microscopic study reveals that the etching occurs selectively at the defect sites of the wires. This implies that the treated wires have much fewer defects than those of the raw material. We have adopted an electrophoresis method, which is usually used in biosciences, to mount single nanowires onto chosen electrodes of a prototype device. The mounting of the wires was checked using scanning probe microscopes. Compared with the commonly used microactuation method, our method is far more applicable to industrial device fabrication, which may require simultaneous manipulation of a large number of wires.
High performance Feussner-type polarizers based on stretched poly(ethylene-terephthalate) films
Authors: Martı́nez-Antón J. C. , Bernabeu E.
Published: July 2002

Stretched poly(ethylene-terephthalate) films appear to be an interesting optical plastic for use in polarization control devices. By means of stretching ratios its birefringence, in practice, can be tailored from ∼0 to ∼0.17. It has a very wide transmission window (∼0.32–5.70 μm) and good thermal, mechanical, and chemical properties. We propose using it for polarizers based on the Feussner design. By implementing this configuration with a biaxially stretched film, we have obtained a polarizer with an achromatic extinction ratio better than 1 part in 50 000. This is comparable with conventional Glan–Thompson polarizers but with additional advantages. The principal refractive indices of the film (in the 0.43–5.7 μm range) and the operational range of the polarizer presented are also provided.
High optical anisotropy in thin films of polyfluorene and its affect on the outcoupling of light in typical polymer light emitting diode structures
Authors: Tammer M. , Higgins R. W. T. , Monkman A. P.
Published: July 2002

The anisotropic optical response of thin films of the conjugated polymer PF2/6am5 (polyfluorene) is investigated using spectroscopic ellipsometry. The influence of the highly dispersive and anisotropic character of refractive index, found in this work for the π–π* transition region, on the outcoupling efficiency of light emitting devices is calculated by applying a simple ray optics model. Polymer light emitting diodes are constructed using PF2/6am4 and PtOEP doped PF2/6am4 (0.5%, 2%, and 4%) as an active layer and their external quantum efficiency (EQE) measured. Electroluminescence spectra of the doped devices are shifted to red wavelengths. The effect of transferring the emission away from high dispersive wavelengths on the outcoupling efficiency is determined and internal quantum efficiency (IQE) values for all devises are calculated. It is shown, that the increase in IQE by doping with PtOEP of up to 80% is completely accountable to the higher photoluminescence quantum yield of the dye. Accounting properly for the anisotropic optic properties of thin spun cast polymer films shows that the simple 2n2 relationship between IQE and EQE yields a large overestimate of the former.
Simple method to prepare individual suspended nanofibers
Authors: Kim Gyu-Tae , Gu Gang , Waizmann Ulrike , Roth Siegmar
Published: July 2002

A simple and general technique for producing a suspended nanofiber has been developed using coordinate markers and a sacrificial layer of poly(methylmethacrylate). The simple procedure does not involve etching processes or chemical vapor deposition and makes it easier to investigate the physical properties of nanofibers in a suspended configuration. As a demonstration, a suspended carbon nanotube rope was fabricated and Young’s modulus was determined to be 0.4 TPa from the force calibration of an atomic force microscope.
Field emission from well-aligned carbon nanotips grown in a gated device structure
Authors: Tsai C. L. , Chen C. F. , Lin C. L.
Published: July 2002

Vertically well-aligned, high-aspect-ratio carbon nanotips have been directly grown upward on the gated device structure with 4 μm gate aperture. The nanotips rapidly nucleate and grow without any catalyst. In addition, selected area deposition of nanotips is achieved by using a Pt layer as inhibitor in the bias-assisted microwave plasma chemical vapor deposition. The field emission current of nanotips on the gated structure is 154 μA (at a gate-to-cathode voltage of Vgc=50 V). This results from the following reasons: (i) short gate-tips spacing, (ii) small gate aperture, and (iii) the high-aspect ratio of nanotips.
Quantum-confined magneto-Stark effect in diluted magnetic semiconductor coupled quantum wells
Authors: Chang Kai , Xia J. B. , Wu H. B. , Feng S. L. , Peeters F. M.
Published: July 2002

The magneto-Stark effect in a diluted magnetic semiconductor (DMS) coupled quantum well (CQW) induced by an in-plane magnetic field is investigate theoretically. Unlike the usual electro-Stark effects, in a DMS CQW the Lorenz force leads to a spatially separated exciton. The in-plane magnetic field can shift the ground state of the magnetoexciton from a zero in-plane center of mass (CM)/momentum to a finite CM momentum, and render the ground state of magnetoexciton stable against radiative recombination due to momentum conservation.
Explanation for the temperature dependence of the gate current in metal-oxide-semiconductor transistors
Authors: Ghetti Andrea
Published: July 2002

The temperature dependence of hot-electron induced gate current in metal-oxide-semiconductor transistors is investigated by means of Monte Carlo simulation. The Monte Carlo model features an approach to the short range Coulomb interaction that provides a better statistical enhancement of “rare” short range electron-electron scattering (EES) events allowing a much better estimate of the distribution function at high energy. It is demonstrated that the gate current temperature dependence is due to EES. In particular, it is shown that EES efficiency in pushing carrier towards higher energy is independent of the lattice temperature. Therefore, reducing the temperature the number of carriers with energy near the applied drain voltage increases because of the reduced phonon scattering. Thus, a larger number of carriers are pushed by EES above the Si/SiO2 energy barrier for lower lattice temperature.
Emission probabilities of π electrons in carbon naonotubes
Authors: Zhou Gang , Duan Wenhui , Gu Binglin , Kawazoe Yoshiyuki
Published: July 2002

The emission probability of π electrons at the local emission region containing a single carbon atom in capped C(5,5) single-walled carbon nanotubes is investigated from electronic and geometrical effects. Owing to electronic effects, the sequence of magnitude of emission probability of π electrons from various local emission regions at the tip is in descending order of T4 (the link region between the tip and the body), T2 and T3 (the middle regions), T1 (the top region), while that at the body is close to 0 due to geometrical effects. The fluctuation in the emission probabilities of π electrons implies that the total energy distribution of emitted electrons at the tip and the image luminescence from the tip are not uniform in essence. Different from electronic effects, geometrical effects are only crucial to the field emission property, and have less influence on the emission probability of π electrons for capped carbon nanotubes.
Influence of the hole population on the transient reflectivity signal of annealed low-temperature-grown GaAs
Authors: Ortiz V. , Nagle J. , Alexandrou A.
Published: July 2002

We study the influence of the carrier dynamics on the transient reflectivity of low-temperature-grown GaAs samples. We report a precise modeling of the recorded reflectivity data, which exhibit multiexponential decays and changes in sign, using a standard point defect model and taking into account the effects of the band filling, band gap renormalization, and trap absorption. We show that the valence-band hole population plays an important role in the behavior of the signals, and that it must be taken into account in order to optimize low-temperature-grown GaAs-based devices.
Hysteresis of the cantilever shift in ultrasonic force microscopy
Authors: Inagaki K. , Matsuda O. , Wright O. B.
Published: July 2002

We propose a technique based on ultrasonic force microscopy that exploits the hysteresis in cantilever jumping to and from a sample while varying the ultrasonic amplitude. Both the elastic modulus and the work of adhesion can be determined by comparision with a relation derived between their ratio and the cantilever shift at the jump-in point. The method is applied to measurements on an aluminum thin film.
Effect of low-temperature preannealing on laser-annealed p+/n ultrashallow junctions
Authors: Baek Sungkweon , Jang Taesung , Hwang Hyunsang
Published: July 2002

The effect of low-temperature preannealing on ultrashallow p+/n junctions was examined. An ultrashallow junction was formed by means of B2H6 plasma doping at an energy of 500 V. The junction was activated by low-temperature (300–500 °C) annealing, followed by laser annealing. Compared with control samples which were not preannealed, low-temperature preannealing significantly improves junction characteristics, resulting in a reduction in junction depth and a lower leakage current density. A cross-sectional transmission-electron-microscopy analysis confirmed the lower defect density, which explains the lower leakage current. By optimizing the process conditions, excellent electrical characteristics of the p+/n junction, i.e., a junction depth of 28 nm and a sheet resistance of 250 Ω/sq, can be obtained.
Ab initio chemical potentials of solid and liquid solutions and the chemistry of the Earth’s core
Authors: Alfè D. , Gillan M. J. , Price G. D.
Published: July 2002

A general set of methods is presented for calculating chemical potentials in solid and liquid mixtures using ab initio techniques based on density functional theory (DFT). The methods are designed to give an ab initio approach to treating chemical equilibrium between coexisting solid and liquid solutions, and particularly the partitioning ratios of solutes between such solutions. For the liquid phase, the methods are based on the general technique of thermodynamic integration, applied to calculate the change of free energy associated with the continuous interconversion of solvent and solute atoms, the required thermal averages being computed by DFT molecular dynamics simulation. For the solid phase, free energies and hence chemical potentials are obtained using DFT calculation of vibrational frequencies of systems containing substitutional solute atoms, with anharmonic contributions calculated, where needed, by thermodynamic integration. The practical use of the methods is illustrated by applying them to study chemical equilibrium between the outer liquid and inner solid parts of the Earth’s core, modeled as solutions of S, Si, and O in Fe. The calculations place strong constraints on the chemical composition of the core, and allow an estimate of the temperature at the inner-core/outer-core boundary.
High-yield synthesis and one-dimensional structure of C60 encapsulated in single-wall carbon nanotubes
Authors: Smith Brian W. , Russo Richard M. , Chikkannanavar Satishkumar B. , Luzzi David E.
Published: July 2002

A supramolecular assembly comprising C60 molecules inside single-wall carbon nanotubes (SWNTs)–C60@SWNT was synthesized in abundance by a vapor phase method, whereby vaporized C60 molecules permeate the interiors of the nanotube and self-assemble into van der Waals interacting chains. Yields were studied as a function of the various synthesis parameters using a calibrated weight uptake technique. For isochronal experiments, the most important parameters effecting yield under the tested conditions were SWNT purity and annealing temperature. Yields of ∼90% have been achieved and confirmed with direct observation by transmission electron microscopy. Agreement between simulated and empirical selected-area diffraction patterns indicates that the endohedral, one-dimensional C60 lattice is simple, with a lattice parameter of 1.00 nm.
Impact of three-dimensional lateral current flow on ultrashallow spreading resistance profiles
Authors: Clarysse T. , Caymax M. , Vandervorst W.
Published: July 2002

The spreading resistance probe (SRP) is a widely used measurement tool for electrical characterization of Si structures. From the measured spreading resistance depth profile, the underlying electrically active dopant profile can be extracted through the application of a series of specific software corrections. In this letter, it is shown that for sub-100 nm deep structures a new type of correction is needed in order to account for the impact of three-dimensional lateral current flow through the conductive surface sublayers located above the actual measurement depth.
Mechanism of atomic force microscopy anodization lithography on a mixed Langmuir–Blodgette resist of palmitic acid and hexadecylamine on silicon
Authors: Ahn Sang Jung , Jang Yun Kyeong , Lee Haeseong , Lee Haiwon
Published: July 2002

A degradation process of a resist was observed by an atomic force microscope (AFM) during AFM anodization lithography on a mixed Langmuir–Blodgett resist of palmitic acid and hexadecylamine. Based on the observation, we proposed a two-step mechanism as follows: (i) a partial degradation of the resist was first achieved and (ii) silicon oxide started to be grown in the presence of a resist. Lateral force microscopy was accomplished on the patterned area before and after the resist was stripped in order to confirm when the silicon oxide started to be grown in the area. This result provides us with the actual information on the mechanism of the anodization lithography on an organic resist.
Cross sectional studies of buried semiconductor interfaces by means of photoemission microscopy
Authors: Barbo F. , Bertolo M. , Bianco A. , Cautero G. , Fontana S. , Johal T. K. , La Rosa S. , Purandare R. C. , Svetchnikov N. , Franciosi A. , Orani D. , Piccin M. , Rubini S. , Cimino R.
Published: July 2002

An important application of photoemission spectromicroscopy would be to measure heterostructures and semiconductor devices in cross section to directly determine band offsets and band bending. We present here studies of p-n GaAs homojunctions and Al/GaAs Schottky junctions fabricated by molecular-beam epitaxy. Our results suggest that a minimum experimental uncertainty of about 0.15 eV will effect band offset determination. In general, useful quantitative information on the junction electrostatics can be obtained provided that the experimental data are analyzed to substract the diffuse photon background and take into account the intensity profile of the photon spot.
“Resonance” phenomena in thermal diffusion processes in two-layer structures
Authors: Gurevich Yu. G. , Logvinov G. N. , Aguirre N. Muñoz , Pérez L. Martı́nez
Published: July 2002

The dependence on the chopper frequency of the effective thermal diffusivity and effective thermal conductivity in photoacoustic experiments is discussed. The theoretical model of a two-layer structure at rear-surface illumination in the high frequency limit is considered. It is shown that the effective thermal diffusivity presents “resonance” while the effective thermal conductivity sharply changes its magnitude and sign. Such “resonant” behavior strongly depends on the surface thermal conductivities associated with the interface thermal contacts.