Fundamentals of Magnetic Resonance Imaging

Engel, Martin R.

doi:10.1148/radiology.187.1.18

Cited by 4 publications

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“…[1][2][3] It is well known that the rate of first oxide layer growth is limited by O 2 adsorption and shows a phase transition from passive oxidation to active oxidation at 700 -800 C depending on O 2 pressure. [4][5][6] In active oxidation, the etching of a surface with SiO desorption progresses exclusively. Passive oxidation is divided into two regions of Langmuir-type adsorption and two-dimensional (2D) oxide island growth at 600 -650 C. 5,6) According to a dual-oxide-species (DOS) model, 7,8) the extent of surface migration of adsorbed oxygen species is negligibly small in the Langmuir-type adsorption region; thus oxide grows randomly at sites where the dissociative adsorption of O 2 molecules occurs.…”

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confidence: 99%

Temperature Dependence of Oxidation-Induced Changes of Work Function on Si(001)2×1 Surface Studied by Real-Time Ultraviolet Photoelectron Spectroscopy

Ogawa

Takakuwa

2005

Jpn. J. Appl. Phys.

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At the initial stage of oxidation on a Si(001)2×1 surface, real-time ultraviolet photoelectron spectroscopy revealed that the O2 dosage dependences of band bending and work function due to a surface dipole layer show a distinct change with increasing temperature from 300 to 600°C in a Langmuir-type adsorption region, while oxygen uptake curves are almost the same at all temperatures examined. In constant to a dual-oxide-species (DOS) model in which the surface migration of adsorbed oxygen is not considered for Langmuir-type adsorption, the observed changes in work function due to the surface dipole layer mean that adsorbed oxygen can migrate on the surface more frequently with increasing temperature, leading to a decrease in the number of adsorbed oxygen atoms bonded at dimer backbond centers and furthermore a significant structural change of the oxide layer.

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confidence: 99%

Temperature Dependence of Oxidation-Induced Changes of Work Function on Si(001)2×1 Surface Studied by Real-Time Ultraviolet Photoelectron Spectroscopy

Ogawa

Takakuwa

2005

Jpn. J. Appl. Phys.

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“…11 Furthermore, due to mass balance, transport of SiO to the surface would cause either oxide growth at the surface or evaporation of SiO. Evaporation is not likely when using higher oxygen pressures than 0.1 Torr, 37,38 so any SiO reaching the SiO 2 -O 2 interface would react to SiO 2 , causing oxide growth at the surface, which is not the case. The exchange at the interface is more than 30% of the oxide growth 35 and this would give a 75% difference between oxide growth measured as weight increase (0.7 ϫ 16 to 0.3 ϫ 28, where 16 ϭ O and 28 ϭ Si) and the oxide thickness (0.7 ϫ 16).…”

Section: Lack Of Straightforward Mechanism For Dissociation Of O 2 In...mentioning

confidence: 99%

Molecular or Atomic Oxygen as the Transported Species in Oxidation of Silicon

Åkermark¹

2000

J. Electrochem. Soc.

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Oxidation of silicon is one of the most studied oxidation processes, mainly because it is a vital step in the fabrication of data chips for the computer industry. Several review articles have been published, 1-7 and since the end of the 1980s it has been generally accepted that the oxide growth occurs by transport of molecular oxygen through the oxide. This belief originates from the oxidation model proposed by Deal and Grove. 8 The Deal-Grove theory, and thereby the transport of molecular oxygen, cannot explain the initial stage of oxidation and has difficulties explaining the sensitivity of oxidation to interface modifications and contaminants (both in the gas phase and on the surface of the SiO 2 ). Several experimental results and arguments have been used to support molecular oxygen as the transported species. The main experimental results and arguments are 1-7 (i) a linear pressure dependence of the parabolic rate constant over a large range of temperatures and pressures; (ii) the activation energy of oxygen diffusion in SiO 2 is the same as for Ar, since O 2 and Ar have the same diameter; (iii) the lack of a straightforward dissociation mechanism for O 2 in SiO 2 ; and (iv) "conventional physicochemical wisdom." 3 Conventional physicochemical wisdom is based on the reaction order, thermodynamics, and the extreme reactivity of radicals (like atomic oxygen), i.e., that oxygen should react with the oxygen network when transported through the oxide, producing oxygen exchange. However, closer examination of these results does not prove that O 2 is the transported species and does not disfavor atomic oxygen at all as the transported species. Recent experiments have shown that (i) the dissociation rate of the oxygen molecules at the surface of the SiO 2 is much higher than the oxidation rate; 9 (ii) there is a coupling between the dissociation rate and the oxidation kinetics; 10 (iii) the oxygen exchange between O 2 molecules catalyzed by the SiO 2 surface (O 2 } O 2 ) varies with pressure raised to the second power; and (iv) there is an oxygen exchange at the internal interface. 11 The pressure dependency squared of the oxygen exchange (O 2 } O 2 ) indicates that the concentration of atomic oxygen depends linearly on the oxygen pressure and so explains a linear pressure dependency of the parabolic rate constant. All these experimental results favor atomic oxygen as the migrating species. In this study the different experimental results are used to argue for atomic and molecular oxygen, respectively, as the transported species. Each result is discussed as an argument for atomic or molecular oxygen as the transported species and given a mark on a seven-graded scale (ϩϩϩ to ϪϪϪ). Summing up the marks, atomic oxygen receives 17ϩ and 0Ϫ (⌺17ϩ), while molecular oxygen receives 3ϩ and 5Ϫ (⌺2Ϫ), leading us to conclude that atomic oxygen is much more likely to be the transported species. ExperimentalA mass spectrometer setup was used to measure the oxygen exchange between O 2 molecules catalyzed by an SiO 2 surface (O 2 ...

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“…It is well known that SiO 2 films decompose at random off Si surfaces through the formation of voids during heating at about 800 • C [8]. If the shape and position of the voids can be controlled, we can form clean open Si windows at given areas in SiO 2 films.…”

Section: Introductionmentioning

confidence: 99%

Observation and control of Si surface and interface processes for nanostructure formation by scanning reflection electron microscopy

Ichikawa

1999

J. Phys.: Condens. Matter

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We observe the oxidation process on clean Si surfaces using high-resolution scanning reflection electron microscopy and form nanostructures on them using focused electron-beam- (EB-) induced surface reactions. Si thermal oxidation occurs layer by layer, and the interface between the oxide film (<1 nm thickness) and Si substrate becomes atomically abrupt. When the sample is heated to 700-800 °C after being irradiated by the focused EB on the surface at room temperature, SiO2 film is selectively decomposed from the EB-irradiated area, resulting in the exposure of a clean Si substrate. The typical width of the clean Si `open windows' is about 10 nm. Using selective reactions during heating after the deposition of Si and Ge films on the patterned samples, Si nanowires and Ge nanoislands with 10 nm size are formed on Si surfaces. Ga-adsorbed Si nanoareas and Ga nanodots are also formed by selective adsorption of Ga on the Si window areas.

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Fundamentals of Magnetic Resonance Imaging

Cited by 4 publications

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Temperature Dependence of Oxidation-Induced Changes of Work Function on Si(001)2×1 Surface Studied by Real-Time Ultraviolet Photoelectron Spectroscopy

Temperature Dependence of Oxidation-Induced Changes of Work Function on Si(001)2×1 Surface Studied by Real-Time Ultraviolet Photoelectron Spectroscopy

Molecular or Atomic Oxygen as the Transported Species in Oxidation of Silicon

Observation and control of Si surface and interface processes for nanostructure formation by scanning reflection electron microscopy

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