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- Hagiwara, K, et al.
(author)
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Review of particle physics
- 2002
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In: Physical Review D (Particles and Fields). - 0556-2821. ; 66:1
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Research review (peer-reviewed)abstract
- This biennial Review summarizes much of Particle Physics Using data from previous editions, plus 2205 new measurements from 667 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles All the particle properties and search limits are listed in Summary Tables We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors, probability, and statistics This edition features expanded coverage of CP violation in B mesons and of neutrino oscillations For the first time we cover searches for evidence of extra dimensions (both in the particle listings and in a new review) Another new review is on Grand Unified Theories A booklet is available containing the Summary Tables and abbreviated versions of some of the other sections of this full Review All tables, listings, and reviews (and errata) are also available on the Particle Data Group website http //pdg 1b1 gov.
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- Ahuja, Rajeev, et al.
(author)
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Optical properties of 4H-SiC
- 2002
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:4, s. 2099-2103
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Journal article (peer-reviewed)abstract
- The optical band gap energy and the dielectric functions of n-type 4H-SiC have been investigated experimentally by transmission spectroscopy and spectroscopic ellipsometry and theoretically by an ab initio full-potential linear muffin-tin-orbital method. We present the real and imaginary parts of the dielectric functions, resolved into the transverse and longitudinal photon moment a, and we show that the anisotropy is small in 4H-SiC. The measurements and the calculations fall closely together in a wide range of energies.
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- Edwards, N.V., et al.
(author)
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Optical characterization of wide bandgap semiconductors
- 2000
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In: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 364:1, s. 98-106
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Journal article (peer-reviewed)abstract
- Our work primarily concerns the characterization of wide-gap III-V nitride semiconductors, nondestructively and at variable temperature, with spectroscopic ellipsometry (SE) and reflectometry in the spectral range from 1.5 to 6 eV. In the case of GaN, there are three main concerns associated with such data: (a) the quantification of the dispersion of the index of refraction with energy, (b) the removal of surface overlayers in real-time, and (c) the determination of the variation of valence bands with biaxial stress and the quantification of residual stress in thin films. The SE and reflectance capabilities provide (1) broadband spectra from 1.5 to 6 eV, which yield information about (a) below the bandgap and (b) above it, and (2) high resolution spectra (less than 1 meV at 3.4 eV) in the vicinity of the gap (3.3-3.6 eV), which enables (c). Here we will discuss issues concerning the relation of (c) to GaN material and growth parameters, though similar data for other wide bandgap materials will be discussed where relevant. Specifically, optimal heterostructure design for potential valence band engineering applications will be discussed in the context of trends in residual stress as a function of film thickness, growth temperature and substrate orientation for GaN/AlN/6H-SiC heterostructures. Standard heterostructures are mostly compressive for samples less than about 0.7 µm thick, are tensile up to about 2 µm and then abruptly become less tensile with stress values near 1 kbar thereafter. Additionally, these trends can be circumvented for moderately thick (approximately 2 µm) GaN layers (normally>2 kbar, tensile) by the introduction of a `buried interface' approach, namely, a strain mediating layer (SML) above the standard high-temperature AlN buffer layer designed to yield a range of compressive stresses from 0 to 2 kbar. The strain characteristics but also the growth rates of subsequently deposited nitride layers can be modulated by changing the growth parameters of the SML. This is achieved by in situ techniques during crystal growth without degrading the optical and structural properties of the deposited layer, as confirmed by XRD, SEM, PL, and AFM data taken on the overlying GaN layers. These results are interpreted in terms of coefficient of thermal expansion data for the layers and data concerning the planarization of GaN layers and growth behavior in non-(0001) directions.
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- van Hees, P A W, et al.
(author)
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Low molecular weight organic acid adsorption in forest soils: effects on soil solution concentrations and biodegradation rates
- 2003
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In: Soil Biology and Biochemistry. - 0038-0717 .- 1879-3428. ; 35:8, s. 1015-1026
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Journal article (peer-reviewed)abstract
- Low molecular weight (LMW) organic acids are believed to play a key role in many rhizosphere and pedogenic processes; However, their efficiency is likely to depend on their susceptibility to sorption and biodegradation. The sorption characteristics of three organic acids (citrate, oxalate and acetate) and phosphate were examined over the concentration range 0-1000 muM in three coniferous forest soil profiles. Sorption to the soil's solid phase could be adequately described by the Langmuir equation with sorption capacity following the horizon series: B > C > E > O. The strength of anion sorption followed the series: phosphate > oxalate : citrate > acetate. Calculations indicated that between 50 and 95% (0 and E horizons) and > 93% (13 horizons) of these LMW organic acids entering the soil will become sorbed to the solid phase. The amount of organic acids predicted to be present on the solid phase at typical soil solution concentrations ranged from < 1 to 1100 nmol g(-1) yielding adsorbed-to-solution ratios (adsorption coefficients) of between < 0.1 and 3100. In the case of citrate, sorption to the solid phase significantly reduced its biodegradation potential by 35-99% depending upon the degree and type of sorption surface. The findings of this work are discussed in the context of the quantitative effects of adsorption on organic acids, their ecological functions and role in soil forming processes.
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