Low-order modeling and dynamic characterization of rapid thermal processing

A low-order model of rapid thermal processing (RTP) of semiconductor wafers is derived. The first-principles nonlinear model describes the static and dynamic thermal behavior of a wafer with approximate spatial temperature uniformity undergoing rapid heating and cooling in a multilamp RTP chamber. The model is verified experimentally for a range of operating temperatures from 400° C to 900° C and pressures of 1 Torr and 1 atmosphere in an inert N₂ environment. Theoretical predictions suggest model validity over a still wider range of operating conditions. One advantage of the low-order model over previous high-order and statistical models is that the proposed model contains a small number of fundamental parameters and functions that, if necessary, are easily identifiable. Furthermore, because of reduced computational complexity, the low-order model can be used in real-time predictive applications including signal processing and process control design. In studying and verifying the model, the dynamic behavior of a semiconductor wafer undergoing rapid temperature changes is characterized. Close comparison between theory and experiment in terms of the wafer eigenvalue and dc gain is demonstrated; the strong nonlinear effects of temperature are shown. Convective heat transfer losses are also examined and are shown to increase with radial position on the wafer.     

Magnetic penetration depth in V3Si and LiTi2O4 measured by μSR

Muon spin relaxation (SR) studies have been performed in the normal spinel LiTi₂O₄ and the A-15 superconductor V₃Si to measure the magnetic penetration depth . The relaxation rate(T) 1/² in field-cooled measurements shows a sharp increase belowT _c followed by saturation at low temperatures in both systems. This feature implies an isotropic energy gap without anomalous zeros, and most likelys-wave pairing. The low temperature penetration depth (T 0) is determined to be 2100Å for LiTi₂O₄ and 1300Å for V₃Si respectively. Assuming a clean limit relation ^–2 n _s /m ^*, we derive the Fermi temperatureT _F n _s/ ^2/3 m ^* from the relaxation rate and the Sommerfeld constant asT _F ^3/4–1/4. Unlike conventional superconductors, both LiTi₂O₄ and V₃Si have a large ratio ofT _c /T _F 0.01, only slightly smaller than those ratios in more exotic superconductors.We thank C. Ballard and K. Hoyle for technical assistance. Work at Columbia University is supported by NSF Grant No. DMR-89-13784 and Packard Foundation (YJU). Ames Laboratory is operated for the U. S. Department of Energy by Iowa State University under Contract No. W-7405-Eng-82. Work at Ames was supported by the Director for Energy Research, Office of Basic Energy Sciences.     

Spin gapless semiconductor like Ti2MnAl film as a new candidate for spintronics application

A novel Heusler ferrimagnet Ti₂MnAl film has been grown on Si(001) substrate using magnetron sputtering. Characteristics of its magnetic and transport properties reveal the spin‐gapless‐semiconductor (SGS) nature of the stoichiometric Ti₂MnAl, in agreement with theoretical prediction. The as‐grown SGS‐like Ti₂MnAl film demonstrated high Curie temperature, nearly compensated ferrimagnetic properties with small coercivity and low magnetization. It also showed semiconductor‐like behavior at room temperature allowing good compatibility with commercial Si‐based semiconductor. In this regards, Ti₂MnAl film is a potential candidate material for spintronics application, especially for the minimization of energy consumption of device. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Transformation mechanism of n-butyl terminated Si nanoparticles embedded into Si1−xCx nanocomposites mixed with Si nanoparticles and C atoms

Bright-field transmission electron microscopy (TEM) images, high-resolution TEM (HRTEM) images, and fast-Fourier transformed electron-diffraction patterns showed that n-butyl terminated Si nanoparticles were aggregated. The formation of Si_1−xC_x nanocomposites was mixed with Si nanoparticles and C atoms embedded in a SiO₂ layer due to the diffusion of C atoms from n-butyl termination shells into aggregated Si nanoparticles. Atomic force microscopy (AFM) images showed that the Si_1−xC_x nanocomposites mixed with Si nanoparticles and C atoms existed in almost all regions of the SiO₂ layer. The formation mechanism of Si nanoparticles and the transformation mechanism of n-butyl terminated Si nanoparticles embedded into Si_1−xC_x nanocomposites mixed with Si nanoparticles and C atoms are described on the basis of the TEM, HRTEM, and AFM results. These results can help to improve the understanding of the formation mechanism of Si nanoparticles.     

Establishing norms for age-related changes in proton T1 of human brain tissue in vivo

The goal of this study was to determine the expected normal range of variation in spin-lattice relaxation time (T₁) of brain tissue in vivo, as a function of age. A previously validated precise and accurate inversion recovery method was used to map T₁ transversely, at the level of the basal ganglia, in a study population of 115 healthy subjects (ages 4 to 72; 57 male and 58 female). Least-squares regression analysis shows that T₁ varied as a function of age in pulvinar nucleus (R² = 56%), anterior thalamus (R² = 51%), caudate (R² = 50%), frontal white matter (R² = 47%), optic radiation (R² = 39%), putamen (R² = 36%), genu (R² = 22%), occipital white matter (R² = 20%) (all p < 0.0001), and cortical gray matter (R² = 53%) (p < 0.001). There were no significant differences in T₁ between men and women. T₁ declines throughout adolescence and early adulthood, to achieve a minimum value in the fourth to sixth decade of life, then T₁ begins to increase. Quantitative magnetic resonance imaging provides evidence that brain tissue continues to change throughout the lifespan among healthy subjects with no neurologic deficits. Age-related changes follow a strikingly different schedule in different brain tissues; white matter tracts tend to reach a minimum T₁ value, and to increase again, sooner than do gray matter tracts. Such normative data may prove useful for the early detection of brain pathology in patients.     

In situ observation of dynamics of plasma self-channeling and bulk modification in silica glasses induced by a high-intensity femtosecond laser

The time-resolved dynamics of plasma self-channeling and refractive index bulk modification in silica glasses were first observed in situ using a high-intensity femtosecond (110 fs) Ti:sapphire laser (λ_p=790 nm). Plasma channeling is induced in silica glass at an irradiation higher than an input intensity of 1.5×10¹² W/cm² and photoinduces either the refractive-index modification or optical crack modification. In the domain of refractive-index modification, the lifetime of induced plasma self-channeling was 20 ps and the structural transition time for forming the refractive-index change was 10 ps. In the domain of optical cracks, however, the lifetime of induced plasma formation was 30 ps and the structural transition time for forming the optical cracks was 40 ps. According to electron spin resonance spectroscopic (ESP) measurement, it was found that the defect concentration of the SiE^′ center increased significantly in the refractive index modification region. A maximum value of the refractive-index change Δn was measured to be 1.6×10^-2. The intensity profile of the output beam transmitted through the refractive-index modification showed that the bulk modification produced a permanent optical waveguide. Received: 8 April 2002 / Accepted: 12 April 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +81-48/462-4682, E-mail: shcho@riken.go.jp     

Effect of fluorine in Li1.27Cr0.2Mn0.53O2 cathode for secondary lithium batteries

Fluorine substituted Li_1.27Cr_0.2Mn_0.53O₂ electrode, prepared by sol–gel method, was investigated in the present work. Thermal analysis was done on this cathode material and found to be thermally stable with a loss of weight near 300 °C. Influence of fluorine substitution on the structural and electrochemical properties of the Li_1.27Cr_0.2Mn_0.53O₂ electrode was studied by X-ray diffraction (XRD) and field emission scanning electron microscope. XRD pattern of the fluorine-doped Li_1.27Cr_0.2Mn_0.53O₂ cathode material quenched at 900 °C indicates a phase pure material. The charge–discharge profile of the prepared cathode material showed that the fluorine substitution for oxygen in the cathode material resulted in improved capacity retention. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, December 7–9, 2006.     

Bandgap engineering of self-assembled InAs quantum dots with a thin AlAs barrier

We investigate the effects of a thin AlAs layer with different position and thickness on the optical properties of InAs quantum dots (QDs) by using transmission electron microscopy and photoluminescence (PL). The energy level shift of InAs QD samples is observed by introducing the thin AlAs layer without any significant loss of the QD qualities. The emission peak from InAs QDs directly grown on the 4 monolayer (ML) AlAs layer is blueshifted from that of reference sample by 219 meV with a little increase in FWHM from 42–47 meV for ground state. In contrast, InAs QDs grown under the 4 ML AlAs layer have PL peak a little redshifted to lower energy by 17 meV. This result is related to the interdiffusion of Al atom at the InAs QDs caused by the annealing effect during growing of InAs QDs on AlAs layer.     

Fringe contrast-based 3D profilometry using fringe projection

Quality-guided algorithm is a widely used method in phase unwrapping. This paper shows an accurate quality map based on fringe contrast for 3D shape measurement. Phase-shifted fringe patterns are projected onto an object surface by a programmable liquid crystal projector and recorded by a CCD camera. A wrapped phase map and a fringe contrast map are extracted from the deformed fringe patterns by the phase-shifting technique. Guided by the contrast map, the quality-guided unwrapping algorithm minimizes unwanted shadow and non-uniform surface reflectance effects and is able to retrieve a correct surface profile. Validity of the proposed method is tested on a fish model and a cutting tool specimen.