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Roles of core-shell and -ray kinetics in layered BN -voltaic efficiency
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Image of FIG. 1.
FIG. 1.

The ionization and relaxation of electrons in an α-voltaic. Primary K (1) and L-shell (2) ionization events, secondary δ-ray impact ionization events (3) and Auger K-shell hole relaxation (4), as well as nonradiative relaxations ((5a) and (5b)): electron and hole phonon emissions) are shown. These interactions describe the manner in which charged-pairs are generated in an α-voltaic. The density of states (De ) for c-BN and the ELFs [ ] for c-BN at the L 1 and K-shell 2 (boron) edges. The latter are used in the TPP-2M model 3,4 to describe impact ionization (3) and can be extended to the primary ionizations (1,2). Here, the fraction of (1) to (2) is determined with ECPSSR theory.

Image of FIG. 2.
FIG. 2.

Variations in , the probability that a δ ray of energy causes an ionization with energy less than or equal to EI , for L (top) and K (bottom) shells. Probabilities of 0.5, 0.8, and 0.95 are shown.

Image of FIG. 3.
FIG. 3.

Variations in the ionization cross sections (in atomic units) for boron, nitrogen, and boron nitride as a function of α particle energy (using ECPSSR theory as implemented by ISICS). As it shows, K-shell and boron interactions will dominate for small , and L-shell and nitrogen interactions will dominate for large .

Image of FIG. 4.
FIG. 4.

Variations in and as a function of the . As α particle slows down, it interacts more strongly with the core shell of boron and a large proportion of all ionization events create core-shell holes. The integrated probability shows the average probability for an α-particle entering c-BN with energy and illustrates the benefit of the strengthening core-shell interaction with decreasing particle energy.

Image of FIG. 5.
FIG. 5.

The electronic bandstructure of cubic boron nitride (calculated using VASP). An example of Auger and radiative K-shell hole relaxation modes are shown with the initial (i, j) and final (μ, ν) Auger electron states indicated.

Image of FIG. 6.
FIG. 6.

(a) Variations of the Auger relaxation rate as a function of core-shell hole energy for 83 and 213k meshes, where results for the latter are averaged among the five nearest neighbors. The average rates are also indicated. (b) Variations of the average Auger and scaled Auger relaxation rates as a function of and . Each , extrapolated , and extrapolation method for simulations with , and are listed. The parentheticals (2), (4), and (5) describe the number of convergent simulations with averaged in order to quantify . Note that the behavior at represents the true behavior in the continuum.

Image of FIG. 7.
FIG. 7.

A layered fuel-α-voltaic device integrated with a TEG. The device concentrates the heat generated in the device and funnels it through the TEG in order to meet its thermal requirements and maintain a reasonably efficient life-span.

Image of FIG. 8.
FIG. 8.

Variations in the overall efficiency and for varying fuel layer thicknesses, Lf . Here, is artificially separated from and , ignoring the non-linear interaction between the three terms, such that its rapid decay is illustrated.


Generic image for table
Table I.

List of the relevant efficiencies, their values, and selected, influential terms. is zero by assumption. and are for to 10 μm.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Roles of core-shell and δ-ray kinetics in layered BN α-voltaic efficiency