scholarly journals Metastable Atom Probe for Measurement of Electron Beam Density Profiles

1971 ◽  
Vol 42 (3) ◽  
pp. 315-318
Author(s):  
James M. Lockhart ◽  
Jens C. Zorn
Keyword(s):  
Electron Beam ◽  
Atom Probe ◽  
Metastable Atom ◽  
Density Profiles ◽  
Beam Density

Electron Beam-Induced Deposition for Atom Probe Tomography Specimen Capping Layers

2016 ◽  
Vol 23 (2) ◽  
pp. 321-328 ◽  
Author(s):  
David R. Diercks ◽  
Brian P. Gorman ◽  
Johannes J. L. Mulders
Keyword(s):  
Electron Beam ◽  
Atom Probe Tomography ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Atom Probe ◽  
Near Surface ◽  
Surface Features ◽  
Dicobalt Octacarbonyl ◽  
Electron Beam Induced Deposition

AbstractSix precursors were evaluated for use as in situ electron beam-induced deposition capping layers in the preparation of atom probe tomography specimens with a focus on near-surface features where some of the deposition is retained at the specimen apex. Specimens were prepared by deposition of each precursor onto silicon posts and shaped into sub-70-nm radii needles using a focused ion beam. The utility of the depositions was assessed using several criteria including composition and uniformity, evaporation behavior and evaporation fields, and depth of Ga+ ion penetration. Atom probe analyses through depositions of methyl cyclopentadienyl platinum trimethyl, palladium hexafluoroacetylacetonate, and dimethyl-gold-acetylacetonate [Me2Au(acac)] were all found to result in tip fracture at voltages exceeding 3 kV. Examination of the deposition using Me2Au(acac) plus flowing O2 was inconclusive due to evaporation of surface silicon from below the deposition under all analysis conditions. Dicobalt octacarbonyl [Co2(CO)8] and diiron nonacarbonyl [Fe2(CO)9] depositions were found to be effective as in situ capping materials for the silicon specimens. Their very different evaporation fields [36 V/nm for Co2(CO)8 and 21 V/nm for Fe2(CO)9] provide options for achieving reasonably close matching of the evaporation field between the capping material and many materials of interest.

Use of Metastable Atom Probe for the Study of Electron Dynamics

1971 ◽  
Vol 39 (9) ◽  
pp. 993-996
Author(s):  
J. Thomas Dickinson ◽  
James M. Lockhart ◽  
Jens C. Zorn
Keyword(s):  
Atom Probe ◽  
Metastable Atom ◽  
Electron Dynamics

Self-consistent Vlasov equilibria for intense hollow relativistic electron beams

1974 ◽  
Vol 12 (3) ◽  
pp. 353-364 ◽  
Author(s):  
R. C. Davidson ◽  
C. D. Striffler
Keyword(s):  
Distribution Function ◽  
Electron Beam ◽  
Relativistic Electron ◽  
Electron Distribution Function ◽  
Nonlinear Boundary Conditions ◽  
Skin Depth ◽  
Beam Density ◽  
Positive Ions ◽  
Guide Field ◽  
Characteristic Radius

This paper discusses the procedure for constructing intense hollow relativistic electron beam equilibria within the framework of the steady-state (∂/∂t = 0) Vlasov–Maxwell equations. It is assumed that the electron beam propagates parallel to a uniform axial guide field Bext0 = B0 êz inside a grounded cylindrical conductor, and that the positive ions provide a partially neutralizing background with density n0i(r) = fn0e(r), where f = const. = fractional neutralization. The equilibrium properties are calculated for the specific choice of electron distribution function , where H, Pθ, and Pz are the energy, canonical angular momentum, and axialcanonical momentum, respectively, for an electron moving in the equilibrium fields, and , and P0 are constants. For this choice of distribution function, the mean axial velocity of the electron beam is equal to , and the beam density profile is hollow with inner and outer radii, R0 and R1, determined self-consistently from nonlinear boundary conditions that involve the equilibrium parameters Po, γb, γ0, etc., and the equilibrium self fields. Closed expressions for Ro and B1 are obtained for the case where the collisionless skin depth c/ωpe is large in comparison with the characteristic radius of the electron beam, and the beam density is sufficiently low that . The two cases, Po>0 and Po<0, are considered.

Interplay between eutectic and dendritic growths dominated by Si content for Nb-Si-Ti alloys via rapid solidification

2021 ◽  
pp. 1-20
Author(s):  
Yueling Guo ◽  
Lina Jia ◽  
Junyang He ◽  
Siyuan Zhang ◽  
Zhiming Li ◽  
...  
Keyword(s):  
Electron Beam ◽  
Rapid Solidification ◽  
Atom Probe ◽  
Ti Alloys ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Beam Surface ◽  
Si Content ◽  
Design And Manufacture ◽  
Fully Lamellar

Abstract Rapid solidification techniques such as electron beam additive manufacturing are considered as promising pathways for manufacturing Nb-Si based alloys for ultra-high-temperature applications. Here we investigate the microstructure diversity of a series of Nb-Si-Ti alloys via electron beam surface melting (EBSM) to reveal their rapid solidification behaviors. Results show that the microstructural transition from coupled to divorced Nbss/Nb3Si eutectics can be triggered by increasing Si content. The formation of fully lamellar eutectics, evidenced by scanning transmission electron microscopy and atom probe tomography (APT), is achieved in the EBSM-processed Nb18Si20Ti alloy (at%), in contrast to the hypereutectic microstructures in arc-melted counterparts. The dendritic microstructures containing divorced eutectics are generated with a higher content of Si during rapid solidification. The transition from faceted to non-faceted growth of intermetallic Nb3Si occurs with the formation of primary Nb3Si dendrites. The interplay between eutectic and dendritic growths of silicides is discussed to provide insights for future alloy design and manufacture.

Atom probe tomography assessment of the impact of electron beam exposure on InxGa1−xN/GaN quantum wells

2011 ◽  
Vol 99 (2) ◽  
pp. 021906 ◽  
Author(s):  
Samantha E Bennett ◽  
David W Saxey ◽  
Menno J Kappers ◽  
Jonathan S Barnard ◽  
Colin J Humphreys ◽  
...  
Keyword(s):  
Electron Beam ◽  
Quantum Wells ◽  
Atom Probe Tomography ◽  
Atom Probe ◽  
The Impact

scholarly journals DISTRIBUTION OF THE BEAM DENSITY AT THE TARGET OF SUBCRITICAL FACILITY “NEUTRON SOURCE”

2021 ◽  
pp. 3-10
Author(s):  
I.M. Karnaukhov ◽  
A.Yu. Zelinsky
Keyword(s):  
Electron Beam ◽  
Neutron Source ◽  
Target Surface ◽  
Beam Shape ◽  
Scanning Method ◽  
Beam Density ◽  
Rectangular Beam ◽  
Start Up ◽  
Transportation Channel ◽  
Homogeneous Beam

NSC KIPT subcritical facility “Neutron Source” uses rectangular tungsten or uranium target of 6464 mm top cross-section. To generate maximum neutron flux, prevent overheating of the target and reduce thermal stress during the facility power operation one should provide uniform electron beam distribution at the target top surface. During the facility design three different possibilities of electron beam density redistribution above the target surface were considered. These were the fast beam scanning with two dimensional scanning magnets; the method of uniform beam distribution formation with linear focusing elements (dipole and quadrupole magnets) and nonlinear focusing elements (octupole magnets), when final required rectangular beam shape with homogeneous beam density is formed at target; and combined method, when one forms the small rectangular beam with homogeneous beam density distribution and scan it over the target surface with scanning magnets. In the paper the all three methods are considered and discussed taking into account the layout of the transportation channel of NSC KIPT subcritical facility “Neutron Source”. For the first stage of the facility start-up and pilot operation the fast scanning method was chosen, realised and tested. The results of the beam distribution measurements over the surface of the target during the facility adjustment and start up are presented.

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