Crystallization Processes

Spaepen, Frans; Turnbull, David

doi:10.1016/b978-0-12-558820-1.50007-7

Cited by 74 publications

(23 citation statements)

References 30 publications

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“…As pointed out by Spaepen and Turnbull 20 , ∆G o is not necessarily equal to the free energy change per atom crystallized. If a dangling bond migration event transfers r atoms from the amorphous phase to the crystal, ∆G o will be r times the free energy change per atom crystallized.…”

Section: Kinetic Analysis Of the Dangling Bond Mechanismmentioning

confidence: 99%

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Pressure-enhanced crystallization kinetics of amorphous Si and Ge: Implications for point-defect mechanisms

Lü

Nygren

Aziz

1991

Journal of Applied Physics

153

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The effects of hydrostatic pressure on the solid-phase epitaxial growth (SPEG) rate v of intrinsic Ge(100) and undoped and doped Si(100) into their respective self-implanted amorphous phases are reported. Samples were annealed in a high-temperature, high-pressure diamond anvil cell. Cryogenically loaded fluid Ar, used as the pressure transmission medium, ensured a clean and hydrostatic environment. v was determined by in situ time-resolved visible (for Si) or infrared (for Ge) interferometry. v increased exponentially with pressure, characterized by a negative activation volume of −0.46Ω in Ge, where Ω is the atomic volume, and −0.28Ω in Si. The activation volume in Si is independent of both dopant concentration and dopant type. Structural relaxation of the amorphous phases has no significant effect on v. These and other results are inconsistent with all bulk point-defect mechanisms, but consistent with all interface point-defect mechanisms, proposed to date. A kinetic analysis of the Spaepen–Turnbull interfacial dangling bond mechanism is presented, assuming thermal generation of dangling bonds at ledges along the interface, independent migration of the dangling bonds along the ledges to reconstruct the network from the amorphous to the crystalline structure, and unimolecular annihilation kinetics at dangling bond ‘‘traps.’’ The model yields v = 2 sin(θ)vsnr exp[(ΔSf + ΔSm)/k] exp− [(ΔHf + ΔHm)/kT], where ΔSf and ΔHf are the standard entropy and enthalpy of formation of a pair of dangling bonds, ΔSm and ΔHm are the entropy and enthalpy of motion of a dangling bond at the interface, vs is the speed of sound, θ is the misorientation from {111}, and nr is the net number of hops made by a dangling bond before it is annihilated. It accounts semiquantitatively for the measured prefactor, orientation dependence, activation energy, and activation volume of v, and the pressure of a ‘‘free-energy catastrophe’’ beyond which the exponential pressure enhancement of SPEG cannot continue uninterrupted due to a vanishing barrier to dangling bond migration. The enhancement of v by doping can be accounted for by an increased number of charged dangling bonds, with no change in the number of neutrals, at the interface. Quantitative models for the doping dependence of v are critically reviewed. At low concentrations the data can be accounted for by either the fractional ionization or the generalized Fermi-level-shifting models; methods to further test these models are enumerated. Ion irradiation may affect v by altering the populatio

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Section: Kinetic Analysis Of the Dangling Bond Mechanismmentioning

confidence: 99%

“…Thus the pressure dependence of a kinetic process, which bears directly on the atomistic mechanism, provides a unique additional parameter for its determination. According to the theory of thermally activated growth [18][19][20] , the growth rate is generally described by:…”

Section: Introductionmentioning

confidence: 99%

Pressure-enhanced crystallization kinetics of amorphous Si and Ge: Implications for point-defect mechanisms

Lü

Nygren

Aziz

1991

Journal of Applied Physics

153

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“…This kind of energy transfer does not normally lead to atom displacements but may damage the target due to beam-stimulated local chemical reactions. [108][109][110][111] The cross sections of both nuclear and electron scattering decreases with increasing electron energy. Both electron and ion beams can be focused onto an area of several nanometers ͑and even down to 0.6 Å in some TEMs͒, which makes it possible to create defects in predetermined areas of the sample.…”

Section: A Production Of Defects In Bulk Targetsmentioning

confidence: 99%

Ion and electron irradiation-induced effects in nanostructured materials

Krasheninnikov¹,

Nordlund²

2010

Journal of Applied Physics

947

591

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A common misconception is that the irradiation of solids with energetic electrons and ions has exclusively detrimental effects on the properties of target materials. In addition to the well-known cases of doping of bulk semiconductors and ion beam nitriding of steels, recent experiments show that irradiation can also have beneficial effects on nanostructured systems. Electron or ion beams may serve as tools to synthesize nanoclusters and nanowires, change their morphology in a controllable manner, and tailor their mechanical, electronic, and even magnetic properties. Harnessing irradiation as a tool for modifying material properties at the nanoscale requires having the full microscopic picture of defect production and annealing in nanotargets. In this article, we review recent progress in the understanding of effects of irradiation on various zero-dimensional and one-dimensional nanoscale systems, such as semiconductor and metal nanoclusters and nanowires, nanotubes, and fullerenes. We also consider the two-dimensional nanosystem graphene due to its similarity with carbon nanotubes. We dwell on both theoretical and experimental results and discuss at length not only the physics behind irradiation effects in nanostructures but also the technical applicability of irradiation for the engineering of nanosystems.

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“…It is also possible that amorphous-like material is present between nanocrystalline grains. Research has shown that the structure of the intergranular phase in nanocrystalline silicon is similar to that of bulk amorphous silicon [28] and amorphous material has long been observed following short pulsed laser irradiation [29,30]. Selected area diffraction indicates that the substrate below the disordered layer is undisturbed crystalline silicon.…”

Section: Surface Layer Structurementioning

confidence: 99%

Microtextured Silicon Surfaces for Detectors, Sensors & Photovoltaics

Carey¹,

Mazur²

2005

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Executive SummaryWith support from this award we studied a novel silicon microtexturing process and its application in silicon-based infrared photodetectors. By irradiating the surface of a silicon wafer with intense femtosecond laser pulses in the presence of certain gases or liquids, the originally shiny, flat surface is transformed into a dark array of microstructures. The resulting microtextured surface has near-unity absorption from near-ultraviolet to infrared wavelengths well below the band gap. The high, broad absorption of microtextured silicon could enable the production of silicon-based photodiodes for use as inexpensive, room-temperature multi-spectral photodetectors. Such detectors would find use in numerous applications including environmental sensors, solar energy, and infrared imaging.The goals of this study were to learn about microtextured surfaces and then develop and test prototype silicon detectors for the visible and infrared. We were extremely successful in achieving our goals. During the first two years of this award, we learned a great deal about how microtextured surfaces form and what leads to their remarkable optical properties. We used this knowledge to build prototype detectors with high sensitivity in both the visible and in the near-infrared. We obtained room-temperature responsivities as high as 100 A/W at 1064 nm, two orders of magnitude higher than standard silicon photodiodes. For wavelengths below the band gap, we obtained responsivities as high as 50 mA/W at 1330 nm and 35 mA/W at 1550 nm, close to the responsivity of InGaAs photodiodes and five orders of magnitude higher than silicon devices in this wavelength region.The following Project Summary includes: Summary of important resultsPrior to receipt of this contract, we developed a process for microtexturing silicon surfaces with laser-assisted etching [1, 2]. The silicon sample is irradiated with a train of high-power ultrashort (100 fs) laser pulses in the presence of SF 6 or Cl 2 . Where the laser strikes the surface, material is etched away in a pattern of conical spikes, with the spike tips at the level of the unetched surface and the spike bases tens of microns below the surface. The surrounding non-irradiated silicon is unaffected, so areas as small as tens of microns on a side can be made. Figure 1 shows a scanning electron micrograph of a microtextured silicon surface.After etching, the silicon surface appears black to the eye (see Figure 2), and the surface absorbs over 90% of incident light from 0.25 µm to 2.5 µm [3]. Flat crystalline silicon absorbs only about 65% of incident light for wavelengths shorter than 1 µm, and absorbs less than 20% at longer wavelengths, with very low absorptance from 1.1 to 1.4 µm. Creation of a prototype microtextured silicon based p-i-n detector.Much of the work done in Year One and Year Two characterized the effects of laser fluence, shot number, gas pressure, and ambient gas on the absorption properties of microtextured silicon [4][5][6][7]. Using this data, we attempted to make...

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Crystallization Processes

Cited by 74 publications

References 30 publications

Pressure-enhanced crystallization kinetics of amorphous Si and Ge: Implications for point-defect mechanisms

Pressure-enhanced crystallization kinetics of amorphous Si and Ge: Implications for point-defect mechanisms

Ion and electron irradiation-induced effects in nanostructured materials

Microtextured Silicon Surfaces for Detectors, Sensors & Photovoltaics

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