Growth Mechanism of Si-Faceted Dendrites

Fujiwara, Kozo; Maeda, Kensaku; Usami, Noritaka; Nakajima, Kazuo

doi:10.1103/physrevlett.101.055503

Cited by 80 publications

(82 citation statements)

References 25 publications

(36 reference statements)

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“…For example, our simulation predicts that a measurement of the ground-state antihydrogen atom yield as a function of the positron plasma temperature at a positron plasma density n e ≃ 10 14 m −3 would show a weaker power-law scaling behaviour than that of three-body recombination. It is noted that the positron temperature dependence of antihydrogen formation was measured at positron density n e ≃ 10 14 m −3 , and an observed scaling behaviour of T −1.1±0.5 e was reported [4] by the ATHENA collaboration, which is consistent with the direction of our prediction qualitatively. …”

Section: Discussionsupporting

confidence: 80%

Antihydrogen Formation and Level Population Evolution During Passage Through a Positron Plasma

Radics¹,

Murtagh²,

Yamazaki³

et al. 2017

Proceedings of the 12th International Conference on Low Energy Antiproton Physics (LEAP2016)

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Antihydrogen is at the focus of antimatter research. One of the main aims is to perform a direct test of the fundamental CPT symmetry by comparing the spectroscopic properties of the ground-state antihydrogen atom with those of the hydrogen atom. In current experiments synthetized antihydrogen is formed mainly via the three-body recombination process after mixing positron and antiproton clouds together in a cryogenic trap. The major three-body formation process populates mainly highly excited Rydberg states, therefore before the antihydrogen atoms reach the ground-state additional processes may take place, such as collisional (de)excitation, ionization and spontaneous or stimulated radiative transitions. We have used a classical-trajectory Monte Carlo (CTMC) code along with regular atomic codes to generate a scattering database of rate coefficients in various experimentally achievable magnetic field strengths and in low temperature positron plasma conditions. We used these rates to calculate the evolution of level population of antihydrogen during formation, scattering and flight within our experimental conditions [1]. The model and the results are presented.

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Section: Discussionsupporting

confidence: 80%

Antihydrogen Formation and Level Population Evolution During Passage Through a Positron Plasma

Radics¹,

Murtagh²,

Yamazaki³

et al. 2017

Proceedings of the 12th International Conference on Low Energy Antiproton Physics (LEAP2016)

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“…The reentrant corners give incorporation sites that favor growth over sites on singular surfaces. Fujiwara, et al, 22 have extended those earlier works with observations and analysis of dendritic silicon crystallizing from the melt at the 100 μm to millimeter scale. For the nanoplatelets reported here, several lines of evidence point to them also growing by a twin-boundary catalyzed dendritic growth mechanism, though at much finer length scales: The facets commonly have 120 • and 60 • angles, observed for example in Figs.…”

confidence: 90%

“…2 While the growth of thin silicon and germanium sheets, catalyzed at the edges of {111} twin planes, has been known for some time, [17][18][19][20][21] reports on this mechanism for silicon typically deal with crystallization from the melt at length scales of 100 μm to 1 mm. 22 At smaller scales, diamond nanoplatelets having 10-nm-scale thicknesses and 100-nm-scale extents have been reported, apparently also catalyzed by twin planes. 23 Here we report results from a 71-growth survey of titanium-catalyzed silicon nanowire growth conditions with atmosperic-pressure chemical vapor deposition (CVD).…”

mentioning

confidence: 99%

Titanium catalyzed silicon nanowires and nanoplatelets

et al. 2013

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Silicon nanowires, nanoplatelets, and other morphologies resulted from silicon growth catalyzed by thin titanium layers. The nanowires have diameters down to 5 nm and lengths to tens of micrometers. The two-dimensional platelets, in some instances with filigreed, snow flake-like shapes, had thicknesses down to the 10 nm scale and spans to several micrometers. These platelets grew in a narrow temperature range around 900 celsius, apparently representing a new silicon crystallite morphology at this length scale. We surmise that the platelets grow with a faceted dendritic mechanism known for larger crystals nucleated by titanium silicide catalyst islands

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“…This production method resulted in antihydrogen atoms which survived for much longer (on the order of hundreds of microseconds) than in-flight antihydrogen. Moreover, both ATHENA and ATRAP were able to obtain high antihydrogen production rates (with peak rates on the order of hundreds per second) [38,39], which allowed for the detailed study of the formation temperature [40,41] and cooling dynamics [42], as well as for the investigation of modulated [43] and stimulated [44,45] formation. The ATHENA apparatus also contained a versatile antihydrogen detector, allowing for the three-dimensional imaging of antiproton annihilations [46], which was, in turn, used to study the spatial and temperature profile of the produced antihydrogen distribution [47].…”

Section: Gravitational Interaction Between Matter and Antimattermentioning

confidence: 99%

Detection of Trapped Antihydrogen

Hydomako

2013

Springer Theses

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The ALPHA experiment is an international effort to produce, trap, and perform precision spectroscopic measurements on antihydrogen (the bound state of a positron and an antiproton). Based at the Antiproton Decelerator (AD) facility at CERN, the ALPHA experiment has recently magnetically confined antihydrogen atoms for the first time. A crucial element in the observation of trapped antihydrogen is ALPHA's silicon vertexing detector. This detector contains sixty silicon modules arranged in three concentric layers, and is able to determine the three-dimensional location of the annihilation of an antihydrogen atom by reconstructing the trajectories of the produced annihilation products.This dissertation focuses mainly on the methods used to reconstruct the annihilation location. Specifically, the software algorithms used to identify and extrapolate charged particle tracks are presented along with the routines used to estimate the annihilation location from the convergence of the identified tracks. It is shown that these methods can determine the annihilation location with a spatial resolution between about 0.6 to 0.8 cm (depending on the coordinate being measured). Furthermore, a robust analysis to identify and reduce cosmic ray background events is described. The cosmic ray background can obscure the trapped antihydrogen signal, and its suppression leads to a significant increase in the annihilation detection sensitivity. The background suppression analysis involves examining the reconstructed detector event based on several selection criteria, including: the number of charged particle tracks, the radial vertex position, and a fit of a straight line to the event hit positions. By carefully optimizing these criteria, (99.54 ± 0.02)% of cosmic ray events are rejected, while (64.4 ± 0.1)% of antihydrogen annihilation events are retained. Finally, the experimental results demonstrating the first-ever magnetic confinement of antihydrogen atoms are presented. These results rely heavily on the silicon i detector, and as such, the role of the annihilation vertex reconstruction is emphasized.

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Growth Mechanism of Si-Faceted Dendrites

Cited by 80 publications

References 25 publications

Antihydrogen Formation and Level Population Evolution During Passage Through a Positron Plasma

Antihydrogen Formation and Level Population Evolution During Passage Through a Positron Plasma

Titanium catalyzed silicon nanowires and nanoplatelets

Detection of Trapped Antihydrogen

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