High-resolution Cross Sections Research Articles

Growth and Characterization of Alternative Gate Dielectrics by Molecular-Beam Epitaxy

In this work, we have investigated conditions to grow epitaxial La2O3 and Sc2O3 thin films directly on (111) Si as well as epitaxial LaScO3 thin films on (100) Si using an alkaline earth oxide buffer layer. The films were structurally characterized by reflection high-energy electron diffraction (RHEED) during growth and four-circle x-ray diffraction (XRD) and high-resolution plan-view and cross-section TEM, including Z-contrast TEM after growth. The epitaxial La2O3 thin films grew with the following epitaxial relationship (0001) La2O3 // (111) Si La2O3 // [112] Si with 1 additional rotational twin variant. Sc2O3 thin films grew epitaxially with a cube-on-cube orientation relationship on (111) silicon. It was not possible to achieve epitaxial LaScO3 thin films without the use of an alkaline earth buffer layer. The epitaxial orientation relationship between the orthorhombic LaScO3 and the underlying Si was (101) LaScO3 // (001) Si and [010] LaScO3 // [110] Si.

First airborne water vapor lidar measurements in the tropical upper troposphere and mid-latitudes lower stratosphere: accuracy evaluation and intercomparisons with other instruments

Abstract. In the tropics, deep convection is the major source of uncertainty in water vapor transport to the upper troposphere and into the stratosphere. Although accurate measurements in this region would be of first order importance to better understand the processes that govern stratospheric water vapor concentrations and trends in the context of a changing climate, they are sparse because of instrumental shortcomings and observational challenges. Therefore, the Falcon research aircraft of the Deutsches Zentrum für Luft- und Raumfahrt (DLR) flew a zenith-viewing water vapor differential absorption lidar (DIAL) during the Tropical Convection, Cirrus and Nitrogen Oxides Experiment (TROCCINOX) in 2004 and 2005 in Brazil. The measurements were performed alternatively on three water vapor absorption lines of different strength around 940 nm. These are the first aircraft DIAL measurements in the tropical upper troposphere and in the mid-latitudes lower stratosphere. Sensitivity analyses reveal an accuracy of 5% between altitudes of 8 and 16 km. This is confirmed by intercomparisons with the Fast In-situ Stratospheric Hygrometer (FISH) and the Fluorescent Advanced Stratospheric Hygrometer (FLASH) onboard the Russian M-55 Geophysica research aircraft during five coordinated flights. The average relative differences between FISH and DIAL amount to −3%±8% and between FLASH and DIAL to −8%±14%, negative meaning DIAL is more humid. The average distance between the probed air masses was 129 km. The DIAL is found to have no altitude- or latitude-dependent bias. A comparison with the balloon ascent of a laser absorption spectrometer gives an average difference of 0%±19% at a distance of 75 km. Six tropical DIAL under-flights of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board ENVISAT reveal a mean difference of −8%±49% at an average distance of 315 km. While the comparison with MIPAS is somewhat less significant due to poorer comparison conditions, the agreement with the in-situ hygrometers provides evidence of the excellent quality of FISH, FLASH and DIAL. Most DIAL profiles exhibit a smooth exponential decrease of water vapor mixing ratio in the tropical upper troposphere to lower stratosphere transition. The hygropause with a minimum mixing ratio of 2.5 µmol/mol is found between 15 and 17 km. A high-resolution (2 km horizontal, 0.2 km vertical) DIAL cross section through the anvil outflow of tropical convection shows that the ambient humidity is increased by a factor of three across 100 km.

Cu-Zn 合金膜の電気抵抗と付着力

Dilute Cu-TM alloy films (TM=Ni, Ti, Mn, Zn, Mg) were investigated in order to develop interconnect lines with low resistivity, high thermal stability and high adhesion to a glass substrate for the installation of an advanced thin film transistor (TFT)-liquid crystal display (LCD). We found that among these added impurities, Zn showed the lowest resistivity 2.8 μΩcm by adding less than 1 at% on annealing above 350°C. Most of these dilute Cu alloy films except for Cu-Zn and Cu-Mn alloys show the formation of thermally grown hillocks on annealing above 300°C. It was also found that the dilute Cu-Zn alloy films showed the highest adhesion to a glass substrate among present alloy systems. The high resolution EDS analysis of the cross section of the films after the 400°C anneal shows not only a large segregation of Zn atoms at the interface between film and glass substrate, but also a relatively high concentration of Zn atoms at both free surface and grain boundaries. However, any precipitation of oxides, such as ZnO was not observed at the interface between film and glass substrate by using a high resolution cross-section TEM analysis. We conclude from these results that the segregation of Zn atoms in Cu alloy systems plays a large role not only to increase an adhesion to a glass substrate, but also suppress the formation of hillocks at elevated temperatures.

Structural analysis of life tested 1.3 μm quantum dot lasers

We present the results of an accelerated life test study of quantum dot lasers operating at 1310 nm. The devices were run at 1 and 2 kA/cm2 (∼10 and ∼70 times Ith, depending on facet coatings), at temperatures of 80 and 100 °C for 1350 h. Some devices, particularly those with higher current densities, showed significant drops in output power and increase in threshold current over this time. The devices were examined using electroluminescence, which shows nonradiative recombination centers in the active region of the device as dark spots. A clear correlation between the density of dark spots and degradation is observed. The defect structure responsible for the dark spots has been identified using conventional and high-resolution cross-section transmission electron microscopy of selected structures. The defects consist of an inverted stacking fault pyramid or microtwin enclosing the dot. The more extensive defects observed after the life test are consistent with their growth by climb, i.e., addition and/or removal of point defects. It is proposed that quantum dot devices show enhanced resistance to the growth of these defects in comparison with quantum well lasers.

Reconstruction of rat artery based on high resolution cross-section images data

目的 基于微米级大鼠断层图片数据集,建立高精度的大鼠动脉血管的三维模型,为各种监测鼠血管组织形态变化的试验提供客观依据.方法 采用一套高分辨率大鼠断层切片图像数据集,使用半自动交互方法对动脉血管进行分割,使用改进的移动立方体(marching cube,MC)算法,在一台IBM图形工作站上对80 Gbyte大小的血管图片数据集进行重建.结果 建立了完整的高精度大鼠动脉血管的三维表面模型,能显示出0.4 mm大小的微细血管.结论 该大鼠动脉血管三维模型可以为观测试验鼠血管组织形态变化提供一个立体的空间比较标准。

Investigation of the formaldehyde differential absorption cross section at high and low spectral resolution in the simulation chamber SAPHIR

Abstract. The results from a simulation chamber study on the formaldehyde (HCHO) absorption cross section in the UV spectral region are presented. We performed 4 experiments at ambient HCHO concentrations with simultaneous measurements of two DOAS instruments in the atmosphere simulation chamber SAPHIR in Jülich. The two instruments differ in their spectral resolution, one working at 0.2 nm (broad-band, BB-DOAS), the other at 2.7 pm (high-resolution, HR-DOAS). Both instruments use dedicated multi reflection cells to achieve long light path lengths of 960 m and 2240 m, respectively, inside the chamber. During two experiments HCHO was injected into the clean chamber by thermolysis of well defined amounts of para-formaldehyde reaching mixing rations of 30 ppbV at maximum. The HCHO concentration calculated from the injection and the chamber volume agrees with the BB-DOAS measured value when the absorption cross section of Meller and Moortgat (2000) and the temperature coefficient of Cantrell (1990) were used for data evaluation. In two further experiments we produced HCHO in-situ from the ozone + ethene reaction which was intended to provide an independent way of HCHO calibration through the measurements of ozone and ethene. However, we found an unexpected deviation from the current understanding of the ozone + ethene reaction when CO was added to suppress possible oxidation of ethene by OH radicals. The reaction of the Criegee intermediate with CO could be 240 times slower than currently assumed. Based on the BB-DOAS measurements we could deduce a high-resolution cross section for HCHO which was not measured directly so far.

Absolute photoionization cross sections with ultra-high energy resolution for Ar, Kr, Xe and N 2 in inner-shell ionization regions

The high-resolution absolute photoionization cross sections for Ar, Kr, Xe and N 2 in the inner-shell ionization region have been measured using a multi-electrode ion chamber and monochromatized synchrotron radiation. The energy ranges of the incident photons for the target gases were as follows: Ar: 242–252 eV (2p Rydberg excitation), Kr: 1650–1770 eV (near the 2p ionization thresholds), Xe: 665–720 eV (near the 3d ionization thresholds) and 880–1010 eV (near the 3p ionization thresholds), N 2: 400–425 eV (N 1s excitation and ionization). It is the first time to measure the absolute ionization cross sections of Ar, Kr, Xe and N 2 over the present energy ranges with the energy resolution of over 10,000. The natural lifetime widths of 2 p 3 / 2 − 1 4 s , 2 p 3 / 2 − 1 3 d , 2 p 3 / 2 − 1 4 d and 2 p 1 / 2 − 1 4 s resonances for Ar, 3 d 5 / 2 − 1 6 p resonance for Xe, and 1 s − 1 π g * ( v ′ = 0 ) resonance for N 2 have been obtained based on the cross sections determined. The ionization energies into the Ar + ( 2 p 3 / 2 − 1 ), Ar + ( 2 p 1 / 2 − 1 ) and Xe + ( 3 d 5 / 2 − 1 ) ionic states are also determined using the Rydberg formula.

Epitaxial growth and formation of interfacial misfit array for tensile GaAs on GaSb

The authors report the formation of an interfacial misfit (IMF) array in the growth of relaxed GaAs bulk layers on a (001) GaSb surface. Under specific conditions, the high quality IMF array has a period of 5.6nm and can accommodate the 7.78% tensile GaAs∕GaSb lattice mismatch. The misfit site is identified as a 90° edge dislocation using Burger’s circuit theory and confirmed by high-resolution cross-section transmission electron microscopy (TEM) images. The resulting GaAs bulk material is both strain-free and highly crystalline. Plan-view TEM images show threading dislocation density of ∼3×106∕cm2. This material demonstration will enable novel device structures including an embedded GaSb active region in GaAs device matrix.

Nano-graphene growth and texturing by Nd:YAG pulsed laser ablation of graphite on Silicon

Pulsed laser ablation from a rotating graphite target operating both in vacuum (∼10-5 Pa) and in He sustaining gas (∼10 Pa) has been used to grow thin carbon films on Si <100>substrates kept at temperatures from RT to 900 °C. Synchrotron and laboratory X-ray diffraction (XRD), performed at grazing incidence, established the formation of nano-sized graphene structures at higher deposition temperatures (∼800 ÷ 900°C). When the carbon plume was expanding in vacuum, these structures resulted to be formed by few parallel graphene layers, characterised by an oriented growth along the graphene planes, with the axis parallel to the substrate. High resolution (HR) cross section TEM images of C nano-structures on grids or in film/Si substrate confirmed both size and orientation of the graphene nano-particles. The presence of He atmosphere in the reaction chamber changes basically the particle nucleation process: a clustering phenomenon of aromatic structures is promoted in the gas phase also at low temperature. The nano-structured particles, however, are characterised by a round shaped morphology and random orientation. The mass density of deposited films, measured by X-ray reflectivity, is also strongly dependent on the experimental settings: films grown in the inert gas show lower density compared to the vacuum deposited ones. The preferential vertically oriented growth of graphene layers in vacuum and high temperature can be explained as a combined effect of different processes under a fast kinetic mode: thermal surface diffusion, in-plane growth of graphene sheets and line source direction of activated carbon species of the laser plume. He deposited samples are characterised by a different nucleation and growth process and a more complex structure.

Structural characterization of ZnO thin films deposited by dc magnetron sputtering

In this work we present recent results on ZnO thin films grown by dc magnetron sputtering technique at room temperature (RT), focusing on structural and surface characterization using conventional cross-section transmission electron microscopy (XTEM) and high resolution cross section transmission electron microscopy (HRXTEM) in an attempt to understand the thickness influence on film, mechanical and optical properties as well as photoreduction/oxidation conductivity changes. Films were found to be polycrystalline with a columnar mode of growth. For films with thickness over 100 nm, XTEM and HRTEM analysis evidenced the presence of a small grains transition layer near interface with the substrate, feature which plays an important role in ZnO thin films for gas sensing application. The control of such structural parameters is proved to be critical for the improvement of their gas sensing performance.

Usefulness of EUS with double-balloon enteroscopy for diagnosis of small-bowel diseases

Until recently, EUS of the small bowel has been performed only in limited regions because of difficulties in endoscopically approaching the small bowel. Double-balloon enteroscopy (DBE) now permits investigation of the entire small bowel. To evaluate the usefulness of EUS with DBE for diagnosis of small-bowel diseases. Pilot study. All patients were examined at Hiroshima University Hospital. EUS with DBE was performed in 20 consecutively analyzed patients (14 men, 6 women; mean age, 47.6 +/- 3.8 years). DBE was performed to investigate obscure GI bleeding (n = 12), small-bowel diseases suggested by other modalities (n = 7), recurring ileus (n = 1), or follow-up (n = 1). Endoscopic biopsies were performed as clinically indicated. EUS image quality for various types of small-bowel diseases and comparison with abdominal US. Protruding lesions were detected in 7 examinations, ulcerative lesions in 7, and no abnormalities in 7. EUS could be performed in 20 of 21 examinations. These images were adequately detailed evaluations and with more detail than US images in 16 examinations. Small nonblinded study. EUS with DBE offers high-resolution cross-sections of small-bowel lesions and may contribute to the diagnosis of small-bowel diseases.

Raman and TEM studies of Ge nanocrystal formation in SiOx:Ge/SiOx multilayers

AbstractAlternating germanosilicate‐siliconoxide layers of 10‐30 nm thickness were grown on Si substrates by plasma enhanced chemically vapor deposition (PECVD). The compositions of the grown films were determined by X‐ray photoelectron spectroscopy measurements. The films were annealed at temperatures varying from 670 to 1000 °C for 5 to 45 minutes under nitrogen atmosphere. High resolution cross section TEM images, electron diffraction and electron energy‐loss spectroscopy as well as energy‐dispersive X‐ray analysis (EDAX) data confirm presence of Ge nanocrystals in each layer. The effect of annealing on the Ge nanocrystal formation in multilayers was investigated by Raman spectroscopy and Transmission Electron Microscopy (TEM). As the annealing temperature is raised to 850 °C, single layer of Ge nanocrystals observed at lower annealing temperatures is transformed into a double layer with the smaller sized nanocrystals closer to the substrate SiO2 interface. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Atomic oxygen photoionization rates computed with high resolution cross sections and solar fluxes

Accurate knowledge of photoionization rates is fundamental for the study and understanding of gases in the solar system. Past calculations of the photoionization rates of atmospheric gases lack the spectral resolution to accommodate highly structured autoionization features in the photoionization cross section. A new theoretical model of the atomic oxygen photoionization cross section combined with a new solar minimum spectral irradiance model enables calculations at very high spectral resolution (0.001 nm). Our analysis of unattenuated photoionization rates reveals no strong coincidences among myriad bright solar emission lines and autoionization lines in the cross section. However, deeper in the terrestrial atmosphere, opacity effects are significant and the need for high spectral accuracy becomes increasingly important. In our solar minimum example, factor of 3 errors occur when the lower thermospheric photoionization rate of atomic oxygen is computed at 1 nm spectral resolution for both the cross section and solar flux.

Photoabsorption cross section measurements of CO 2 between 106.1 and 118.7 nm at 295 and 195 K

High-resolution vacuum ultraviolet carbon dioxide photoabsorption cross sections are required for modeling airglow emissions from the Martian and Venusian atmospheres and for photochemical models of those atmospheres. We report cross section measurements on CO 2 at 295 and 195 K between 106.1 and 118.7 nm at a spectral resolution of 0.005 nm. Significant deviations from the results of previous, lower-resolution measurements are apparent, particularly in regions of sharp spectral structure. Temperature dependence in the photoabsorption cross sections is evident throughout the region, being especially pronounced at wavelengths greater than 113 nm.

TEM studies of Ge nanocrystal formation in PECVD grownSiO2:Ge/SiO2 multilayers

We investigate the effect of annealing on the Ge nanocrystal formation in multilayeredgermanosilicate–oxide films grown on Si substrates by plasma enhanced chemical vapour deposition(PECVD). The multilayered samples were annealed at temperatures ranging from 750 to900 °C for 5 min under nitrogen atmosphere. The onset of formation of Ge nanocrystals, at750 °C, can be observed via high resolution TEM micrographs. The diameters of Ge nanocrystalswere observed to be between 5 and 14 nm. As the annealing temperature is raised to850 °C, asecond layer of Ge nanocrystals forms next to the original precipitation band, positioning itself closer to thesubstrate SiO2 interface. High resolution cross section TEM images, electron diffraction and electronenergy-loss spectroscopy as well as energy-dispersive x-ray analysis (EDAX) data allindicate that Ge nanocrystals are present in each layer.

High-resolution absolute photoabsorption cross sections for Ne in the 1s2s and 1s2p resonant double excitation

The high-resolution absolute photoabsorption cross sections with an absolute photon energy scale for Ne 1s2p/1s2s double excitation in the energy region of 900–940 eV have been measured using a multi-electrode ionization chamber and monochromatized synchrotron radiation. The Ne [1s2p](3,1P)nln′l′ doubly excited states observed in the energy range of 900–920 eV are analysed with the aid of theoretical calculations based on the multiconfiguration Dirac–Fock method. The second strongest peak in this energy region is assigned to be [1s2p](3P)3p4p.

Petrophysical and seismic properties of lower Eocene clastic rocks in the central Maracaibo Basin

High-resolution, well-log cross sections are used to map the continuity of hydrocarbon-bearing sandstone reservoirs in the Centro Lago fields, central Maracaibo Basin, Venezuela. Because most sandstone reservoirs are below the limit of seismic resolution, reservoir mapping relies on detailed well-log correlations. Seismic data are used mainly to define the structural framework. A feasibility analysis based on the correlation of seismic data and petrophysical properties of Eocene clastic rocks was conducted to demonstrate that lithology and fluid content can be differentiated by acoustic impedance known from well-log data. However, low vertical resolution of the three-dimensional seismic data made available for this study (25 Hz dominant frequency) is not adequate to constrain the lateral and vertical continuity of the Eocene reservoirs. The main sandstone reservoirs in lower Eocene clastic rocks of the Centro Lago fields are found in distributary channels and tidal sand-bar facies. These reservoirs provide good-quality fluid-flow units. Channel complexes and sand bars are concentrated along the crest of a north-northeast–trending anticline bounded by parallel left-lateral strike-slip faults. Reservoirs are generally compartmentalized by transverse northwest-southeast–striking faults that intersect the main anticlinal axis. Detailed high-resolution well-log cross sections and mapping, integrated with the structural framework interpreted from the seismic data, indicate the presence of untested oil plays in the Centro Lago fields. These new plays are located along the flanks of the main anticline and are found in Eocene tidal bars in the central and northern areas of the Centro Lago fields.

SAOZ measurements of NO2 at Aberystwyth

We present in this paper fifteen years' measurements, from March 1991 to September 2005, of stratospheric NO2 vertical columns measured by a SAOZ zenith-sky visible spectrometer. The instrument spent most of its time at Aberystwyth, Wales, with occasional excursions to other locations. The data have been analysed with the WinDOAS analysis program with low-temperature high-resolution NO2 cross-sections and fitting a slit function to each spectrum. Because of a change in detector in May 1998 there is some uncertainty about the relative changes before and after this date, which are partially constrained by the results of an intercomparison exercise. However, the effect of the Mt Pinatubo aerosol cloud is very evident in the data from 1991-94, with a decrease of 10% in NO2 in the summer of 1992 (the SAOZ was located in Lerwick, Scotland during the winter of 1991-92 and observed very low NO2 values but these cannot be directly compared to the Aberystwyth data). To focus more on interannual and long-term variations in NO2, a seasonal variation comprising an annual and semi-annual component was fitted to the morning and evening twilight separately from 1995 to the present. This fit yielded average NO2 columns of 4.08 x 10(15) cm(-2) and 2.68 x 10(15) cm(-2) for the evening and morning twilight, respectively, with a corresponding annual amplitude of +/-2.08 x 10(15) cm(-2) and +/-1.50 x 10(15) cm(-2). Departures from the fitted curve show a trend of 6% per decade, consistent with that reported elsewhere, for the period 1998-2003, but in the past two years a distinct interannual variation of amplitude of approximately 8% has emerged.

Synthesis and size differentiation of Ge nanocrystals in amorphous SiO2

Germanosilicate layers were grown on Si substrates by plasma enhanced chemical vapor deposition (PECVD) and annealed at different temperatures ranging from 700–1010 °C for durations of 5 to 60 min. Transmission electron microscopy (TEM) was used to investigate Ge nanocrystal formation in SiO2:Ge films. High-resolution cross section TEM images, electron energy-loss spectroscopy and energy dispersive X-ray analysis (EDX) data indicate that Ge nanocrystals are present in the amorphous silicon dioxide films. These nanocrystals are formed in two spatially separated layers with average sizes of 15 and 50 nm, respectively. EDX analysis indicates that Ge also diffuses into the Si substrate.

Gelina neutron target optimisation

A study is being performed on the properties of the Geel Electron Linear Accelerator (GELINA), a powerful white neutron source, designed for the high-energy resolution time-of-flight measurements. The main aim of this study is to reduce the time spread of neutrons of the given energy without compromising the neutron yield. Both time spread and neutron intensity influence the experimental accuracy of high-resolution neutron cross section measurements, which are particularly important in the resonance region. The quantities of interest have been simulated with coupled electron-photon-neutron steady state and transient MCNP4C3 calculations. Following benchmarking of the code to the properties of the existing target, neutron yield, energy spectra, resolution functions, and neutron and heat spatial distributions have been determined for various alternative geometries and materials. At a fixed accelerator power, actinides deliver the highest neutron yield and a small target provides the best time resolution. The resulting high-power density requires a joint optimisation of the thermal hydraulics and neutronics properties.